feat(ui): refresh auth, entry, admin, and secondary pages

Apply the new design-system primitives across the remaining pages so the
whole app shares one visual language:

- Auth/entry: redesigned index, login, register (centered card layout,
  SVG icons, semantic tokens)
- Admin: sidebar nav with icons, cohesive admin dashboard/users/library/
  processing-issues/settings (tables use border-line + hover states;
  scan/websocket attributes preserved)
- Secondary: analytics (stat cards), devices, progress, conflicts, queue,
  profile + form/modal all migrated to .card/.btn/.input primitives and
  SVG action icons
- Docs + API explorer + setup wizard + collection/rules/modals +
  unlinked books + book-detail modals: consistent chrome, modal scrims
  use --surface-overlay, close buttons use icon-btn
- reader.templ and error.templ intentionally left unchanged

templates/admin_sidebar.templ

@@ -1,23 +1,30 @@
 package templates
 
 templ AdminSidebar(user User, currentPath string) {
-	<aside class="w-64 border-r" style="background-color: var(--bg-secondary); border-color: var(--border)">
-		<div class="p-6">
-			<h2 class="text-lg font-semibold mb-6" style="color: var(--text-primary)">Admin Panel</h2>
-			<nav class="space-y-2">
-				<a href="/admin" class={activeClass(currentPath, "/admin")} style="color: var(--text-primary)">
-					🏠 Dashboard
+	<aside class="w-60 shrink-0 border-r border-line bg-surface-raised">
+		<div class="p-5">
+			<h2 class="mb-5 flex items-center gap-2 text-sm font-bold uppercase tracking-wide text-content-muted">
+				@Icon("shield", "h-4 w-4")
+				Admin
+			</h2>
+			<nav class="space-y-1">
+				<a href="/admin" class={ activeClass(currentPath, "/admin") }>
+					@Icon("home", "h-4 w-4")
+					Dashboard
 				</a>
-				<a href="/admin/users" class={activeClass(currentPath, "/admin/users")} style="color: var(--text-primary)">
-					👤 User Administration
+				<a href="/admin/users" class={ activeClass(currentPath, "/admin/users") }>
+					@Icon("users", "h-4 w-4")
+					Users
 				</a>
-				<a href="/admin/library" class={activeClass(currentPath, "/admin/library")} style="color: var(--text-primary)">
-					📚 Library Management
+				<a href="/admin/library" class={ activeClass(currentPath, "/admin/library") }>
+					@Icon("library", "h-4 w-4")
+					Libraries
 				</a>
-				<a href="/admin/settings" class={activeClass(currentPath, "/admin/settings")} style="color: var(--text-primary)">
-					⚙️ System Settings
+				<a href="/admin/settings" class={ activeClass(currentPath, "/admin/settings") }>
+					@Icon("settings", "h-4 w-4")
+					Settings
 				</a>
 			</nav>
 		</div>
 	</aside>
-}   
+}