refactor(theme): fix theme consistency and persistence

- Apply server-side theme rendering to authenticated pages
  - bookshelf.templ: use dynamic theme-{ user.Theme }
  - admin pages: use dynamic theme rendering
- Add progressive enhancement for public pages
  - index.templ, login.templ, register.templ: inline localStorage check
  - Prevents theme flash on page load
- Consolidate wood theme logic into theme.ts
  - Move wood gradient handling from header.ts to theme.ts
  - Apply wood themes consistently via applyTheme()
- Export applyTheme to window for use by header.ts
- Fix theme selector by adding theme.js to header template

web/src/header.ts

@@ -27,39 +27,11 @@ const toggleUserMenu = (): void => {
 };
 
 const changeThemeTo = (theme: string): void => {
-    // Apply the theme
-    if (theme.startsWith('wood-')) {
-        // Apply wood background theme
-        document.body.className = `theme-${theme}`;
-        
-        // Set wood background style
-        let woodGradient = '';
-        switch (theme) {
-            case 'wood-light':
-                woodGradient = 'linear-gradient(135deg, #deb887 0%, #d2a679 50%, #c9975b 100%)';
-                break;
-            case 'wood-dark':
-                woodGradient = 'linear-gradient(135deg, #8b7355 0%, #6b5344 50%, #5a4636 100%)';
-                break;
-            case 'wood-mahogany':
-                woodGradient = 'linear-gradient(135deg, #a0522d 0%, #8b4513 50%, #7a3c10 100%)';
-                break;
-        }
-        
-        document.body.style.background = woodGradient;
-        document.body.style.backgroundSize = 'cover';
-        document.body.style.backgroundAttachment = 'fixed';
-    } else {
-        // Apply regular theme
-        document.body.className = `theme-${theme}`;
-        document.body.style.background = '';
-        document.body.style.backgroundSize = '';
-        document.body.style.backgroundAttachment = '';
+    // Apply the theme using the consolidated function from theme.ts
+    if ((window as any).applyTheme) {
+        (window as any).applyTheme(theme);
     }
-    
-    // Save to localStorage
-    localStorage.setItem('theme', theme);
-    
+
     // Save to server if logged in
     const token = localStorage.getItem('token');
     if (token) {
@@ -72,7 +44,7 @@ const changeThemeTo = (theme: string): void => {
             body: JSON.stringify({ theme })
         }).catch(err => console.log('Theme save failed', err));
     }
-    
+
     // Close dropdown
     const dropdown = document.getElementById('theme-dropdown');
     if (dropdown) {