feat(ui): persist library selection across page navigation

Save the selected library to localStorage when the user changes the
dropdown on the bookshelf page, and restore it on every page load via
a new restoreLibrarySelection() call in the header Alpine component.

This ensures that when a user navigates between dashboard, bookshelf,
collections, etc., their last-chosen library filter is automatically
re-applied rather than resetting to the default.

Changes:
- web/src/bookshelf.ts: listen for change events on #library-select
  and persist the value to localStorage
- web/src/header.ts: add restoreLibrarySelection() which checks
  localStorage and sets the matching dropdown option on page load
- templates/header.templ: call restoreLibrarySelection() in x-init
- templates/header_templ.go: regenerated from templ source

templates/header.templ

@@ -1,7 +1,7 @@
 package templates
 
 templ Header(user User, currentPath string) {
-	<nav x-data="header" x-init="initializeSearch(); initializeTheme(); loadWoodPaneling(); updateWoodPanelingIndicators()" class="border-b header-nav" style="border-color: var(--border); background-color: var(--bg-secondary);">
+	<nav x-data="header" x-init="initializeSearch(); initializeTheme(); loadWoodPaneling(); updateWoodPanelingIndicators(); restoreLibrarySelection()" class="border-b header-nav" style="border-color: var(--border); background-color: var(--bg-secondary);">
 		<div x-data="{}" x-init="console.log('Alpine is working!', $el)"></div>
 		<div class="w-full px-4 sm:px-6 lg:px-8">
 			<div class="flex justify-between items-center h-16">

templates/header_templ.go

@@ -29,7 +29,7 @@ func Header(user User, currentPath string) templ.Component {
 			templ_7745c5c3_Var1 = templ.NopComponent
 		}
 		ctx = templ.ClearChildren(ctx)
-		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 1, "<nav x-data=\"header\" x-init=\"initializeSearch(); initializeTheme(); loadWoodPaneling(); updateWoodPanelingIndicators()\" class=\"border-b header-nav\" style=\"border-color: var(--border); background-color: var(--bg-secondary);\"><div x-data=\"{}\" x-init=\"console.log('Alpine is working!', $el)\"></div><div class=\"w-full px-4 sm:px-6 lg:px-8\"><div class=\"flex justify-between items-center h-16\"><!-- Left: App Title & Navigation --><div class=\"flex items-center space-x-6\"><a href=\"/dashboard\" class=\"text-xl font-bold hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); text-decoration: none;\">📚 Bookhoard</a><div class=\"hidden md:flex items-center space-x-4\"><a href=\"/dashboard\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Library</a> <a href=\"/bookshelf\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">All Books</a> <a href=\"/collections\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Collections</a> <a href=\"/progress\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Progress</a> <a href=\"/devices\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Devices</a></div></div><!-- Center: Search Box --><div class=\"flex-1 max-w-2xl mx-8\"><div class=\"relative\"><input type=\"text\" id=\"header-search\" placeholder=\"Search your library...\" class=\"w-full px-4 py-2 pl-10 border rounded-lg\" style=\"background-color: var(--bg-primary); color: var(--text-primary); border-color: var(--border);\" autocomplete=\"off\"> <svg class=\"absolute left-3 top-2.5 h-5 w-5\" style=\"color: var(--text-secondary)\" fill=\"none\" stroke=\"currentColor\" viewBox=\"0 0 24 24\"><path stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z\"></path></svg></div></div><!-- Right: Theme Switcher & User Menu --><div x-data=\"{ themeDropdownOpen: false, userMenuOpen: false }\" class=\"flex items-center space-x-4\"><!-- Theme Switcher --><div class=\"relative\"><button @click=\"themeDropdownOpen = !themeDropdownOpen\" type=\"button\" class=\"p-2 rounded-lg hover:bg-gray-700 transition-colors\" style=\"background-color: var(--bg-primary);\"><svg class=\"h-6 w-6\" style=\"color: var(--text-primary)\" fill=\"none\" stroke=\"currentColor\" viewBox=\"0 0 24 24\"><path stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M7 21a4 4 0 01-4-4V5a2 2 0 012-2h4a2 2 0 012 2v12a4 4 0 01-4 4zm0 0h12a2 2 0 002-2v-4a2 2 0 00-2-2h-2.343M11 7.343l1.657-1.657a2 2 0 012.828 0l2.829 2.829a2 2 0 010 2.828l-8.486 8.485M7 17h.01\"></path></svg></button><div x-show=\"themeDropdownOpen\" @click.outside=\"themeDropdownOpen = false\" x-transition:enter=\"transition ease-out duration-200\" x-transition:enter-start=\"opacity-0 scale-95\" x-transition:enter-end=\"opacity-100 scale-100\" x-transition:leave=\"transition ease-in duration-150\" x-transition:leave-start=\"opacity-100 scale-100\" x-transition:leave-end=\"opacity-0 scale-95\" class=\"absolute right-0 mt-2 w-64 rounded-lg shadow-lg z-50\" style=\"background-color: var(--bg-secondary); border: 1px solid var(--border); display: none;\"><div class=\"p-4\"><h3 class=\"text-sm font-semibold mb-3\" style=\"color: var(--text-primary)\">Select Theme</h3><div class=\"space-y-2\"><button @click=\"changeTheme('tokyo-night'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inline-block w-4 h-4 rounded mr-2\" style=\"background-color: #7aa2f7;\"></span> Tokyo Night</button> <button @click=\"changeTheme('dracula'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inline-block w-4 h-4 rounded mr-2\" style=\"background-color: #bd93f9;\"></span> Dracula</button> <button @click=\"changeTheme('nord'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inline-block w-4 h-4 rounded mr-2\" style=\"background-color: #88c0d0;\"></span> Nord</button> <button @click=\"changeTheme('solarized-dark'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inlLine truncated
+		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 1, "<nav x-data=\"header\" x-init=\"initializeSearch(); initializeTheme(); loadWoodPaneling(); updateWoodPanelingIndicators(); restoreLibrarySelection()\" class=\"border-b header-nav\" style=\"border-color: var(--border); background-color: var(--bg-secondary);\"><div x-data=\"{}\" x-init=\"console.log('Alpine is working!', $el)\"></div><div class=\"w-full px-4 sm:px-6 lg:px-8\"><div class=\"flex justify-between items-center h-16\"><!-- Left: App Title & Navigation --><div class=\"flex items-center space-x-6\"><a href=\"/dashboard\" class=\"text-xl font-bold hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); text-decoration: none;\">📚 Bookhoard</a><div class=\"hidden md:flex items-center space-x-4\"><a href=\"/dashboard\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Library</a> <a href=\"/bookshelf\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">All Books</a> <a href=\"/collections\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Collections</a> <a href=\"/progress\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Progress</a> <a href=\"/devices\" class=\"text-sm hover:opacity-80 transition-opacity\" style=\"color: var(--text-secondary); text-decoration: none;\">Devices</a></div></div><!-- Center: Search Box --><div class=\"flex-1 max-w-2xl mx-8\"><div class=\"relative\"><input type=\"text\" id=\"header-search\" placeholder=\"Search your library...\" class=\"w-full px-4 py-2 pl-10 border rounded-lg\" style=\"background-color: var(--bg-primary); color: var(--text-primary); border-color: var(--border);\" autocomplete=\"off\"> <svg class=\"absolute left-3 top-2.5 h-5 w-5\" style=\"color: var(--text-secondary)\" fill=\"none\" stroke=\"currentColor\" viewBox=\"0 0 24 24\"><path stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z\"></path></svg></div></div><!-- Right: Theme Switcher & User Menu --><div x-data=\"{ themeDropdownOpen: false, userMenuOpen: false }\" class=\"flex items-center space-x-4\"><!-- Theme Switcher --><div class=\"relative\"><button @click=\"themeDropdownOpen = !themeDropdownOpen\" type=\"button\" class=\"p-2 rounded-lg hover:bg-gray-700 transition-colors\" style=\"background-color: var(--bg-primary);\"><svg class=\"h-6 w-6\" style=\"color: var(--text-primary)\" fill=\"none\" stroke=\"currentColor\" viewBox=\"0 0 24 24\"><path stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M7 21a4 4 0 01-4-4V5a2 2 0 012-2h4a2 2 0 012 2v12a4 4 0 01-4 4zm0 0h12a2 2 0 002-2v-4a2 2 0 00-2-2h-2.343M11 7.343l1.657-1.657a2 2 0 012.828 0l2.829 2.829a2 2 0 010 2.828l-8.486 8.485M7 17h.01\"></path></svg></button><div x-show=\"themeDropdownOpen\" @click.outside=\"themeDropdownOpen = false\" x-transition:enter=\"transition ease-out duration-200\" x-transition:enter-start=\"opacity-0 scale-95\" x-transition:enter-end=\"opacity-100 scale-100\" x-transition:leave=\"transition ease-in duration-150\" x-transition:leave-start=\"opacity-100 scale-100\" x-transition:leave-end=\"opacity-0 scale-95\" class=\"absolute right-0 mt-2 w-64 rounded-lg shadow-lg z-50\" style=\"background-color: var(--bg-secondary); border: 1px solid var(--border); display: none;\"><div class=\"p-4\"><h3 class=\"text-sm font-semibold mb-3\" style=\"color: var(--text-primary)\">Select Theme</h3><div class=\"space-y-2\"><button @click=\"changeTheme('tokyo-night'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inline-block w-4 h-4 rounded mr-2\" style=\"background-color: #7aa2f7;\"></span> Tokyo Night</button> <button @click=\"changeTheme('dracula'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inline-block w-4 h-4 rounded mr-2\" style=\"background-color: #bd93f9;\"></span> Dracula</button> <button @click=\"changeTheme('nord'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-primary);\"><span class=\"inline-block w-4 h-4 rounded mr-2\" style=\"background-color: #88c0d0;\"></span> Nord</button> <button @click=\"changeTheme('solarized-dark'); themeDropdownOpen = false\" type=\"button\" class=\"w-full text-left px-3 py-2 rounded hover:opacity-80 transition-opacity\" style=\"color: var(--text-primary); background-color: var(--bg-prLine truncated
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}