feat: add admin menu configuration and sidebar improvements

- Add AdminMenuConfig model for per-platform menu customization
- Add menu registry for centralized menu configuration
- Add my-menu-config and platform-menu-config admin pages
- Update sidebar with improved layout and Alpine.js interactions
- Add FrontendType enum for admin/vendor menu separation
- Document self-contained module patterns in session note

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/admin/js/init-alpine.js

@@ -212,6 +212,69 @@ function data() {
 
     get isSuperAdmin() {
       return this.adminProfile?.is_super_admin === true;
+    },
+
+    // ─────────────────────────────────────────────────────────────────
+    // Dynamic menu visibility (loaded from API)
+    // ─────────────────────────────────────────────────────────────────
+    menuData: null,
+    menuLoading: false,
+    visibleMenuItems: new Set(),
+
+    async loadMenuConfig(forceReload = false) {
+      // Don't reload if already loaded (unless forced)
+      if (!forceReload && (this.menuData || this.menuLoading)) return;
+
+      // Skip if apiClient is not available (e.g., on login page)
+      if (typeof apiClient === 'undefined') {
+        console.debug('Menu config: apiClient not available');
+        return;
+      }
+
+      // Skip if not authenticated
+      if (!localStorage.getItem('admin_token')) {
+        console.debug('Menu config: no admin_token, skipping');
+        return;
+      }
+
+      this.menuLoading = true;
+      try {
+        this.menuData = await apiClient.get('/admin/menu-config/render/admin');
+        // Build a set of visible menu item IDs for quick lookup
+        this.visibleMenuItems = new Set();
+        for (const section of (this.menuData?.sections || [])) {
+          for (const item of (section.items || [])) {
+            this.visibleMenuItems.add(item.id);
+          }
+        }
+        console.debug('Menu config loaded:', this.visibleMenuItems.size, 'items');
+      } catch (e) {
+        // Silently fail - menu will show all items as fallback
+        console.debug('Menu config not loaded, using defaults:', e?.message || e);
+      } finally {
+        this.menuLoading = false;
+      }
+    },
+
+    async reloadSidebarMenu() {
+      // Force reload the sidebar menu config
+      this.menuData = null;
+      this.visibleMenuItems = new Set();
+      await this.loadMenuConfig(true);
+    },
+
+    isMenuItemVisible(menuItemId) {
+      // If menu not loaded yet, show all items (fallback to hardcoded)
+      if (!this.menuData) return true;
+      return this.visibleMenuItems.has(menuItemId);
+    },
+
+    isSectionVisible(sectionId) {
+      // If menu not loaded yet, show all sections
+      if (!this.menuData) return true;
+      // Check if any item in this section is visible
+      const section = this.menuData?.sections?.find(s => s.id === sectionId);
+      return section && section.items && section.items.length > 0;
     }
   }
 }