feat(router): SSR libraries and users on /admin/library page

Update the /admin/library route handler to fetch and pass data to
template for server-side rendering, improving page load performance.

Changes:
- Fetch all libraries using ListLibrariesData() helper
- Fetch all users for visibility management
- Convert database rows to template types (LibraryData, User)
- Pass data to AdminLibrary template for SSR
- Follows existing pattern from dashboard and custom-section pages

Benefits:
- Faster initial page load (no AJAX fetch)
- Better UX (content visible immediately)
- Progressive enhancement (works without JS)

internal/router/frontend.go

@@ -413,8 +413,47 @@ func registerFrontendRoutes(cfg *Config) {
 		if err != nil {
 			return renderErrorPage(c, "Error loading user", "user_load_error")
 		}
+
+		// Fetch all libraries (admin-only)
+		libraries, err := cfg.LibraryHandler.ListLibrariesData(c.Request().Context())
+		if err != nil {
+			log.Printf("ListLibrariesData failed: %v", err)
+			libraries = []database.ListLibrariesRow{}
+		}
+
+		// Convert to template LibraryData
+		libData := make([]templates.LibraryData, len(libraries))
+		for i, lib := range libraries {
+			libUUID, _ := uuid.FromBytes(lib.ID.Bytes[0:16])
+			libData[i] = templates.LibraryData{
+				ID:          libUUID.String(),
+				Name:        lib.Name,
+				Description: getText(lib.Description),
+				TypeName:    lib.TypeName,
+			}
+		}
+
+		// Fetch all users for visibility management
+		users, err := cfg.Queries.ListUsers(c.Request().Context())
+		if err != nil {
+			log.Printf("ListUsers failed: %v", err)
+			users = []database.ListUsersRow{}
+		}
+
+		// Convert to template User types
+		userData := make([]templates.User, len(users))
+		for i, u := range users {
+			userUUID, _ := uuid.FromBytes(u.ID.Bytes[0:16])
+			userData[i] = templates.User{
+				ID:       userUUID.String(),
+				Username: u.Username,
+				Email:    u.Email,
+				Role:     u.Role,
+			}
+		}
+
 		var buf bytes.Buffer
-		err = templates.AdminLibrary(user).Render(c.Request().Context(), &buf)
+		err = templates.AdminLibrary(user, libData, userData).Render(c.Request().Context(), &buf)
 		if err != nil {
 			return err
 		}