feat: Add Plugin Marketplace and My Plugins management pages

This commit completes the plugin system UI by adding two key pages:

1. Plugin Marketplace (/plugins/marketplace):
   - Browse and search platform-provided plugins
   - Filter by category (EMAIL, REPORTS, CUSTOMER, BOOKING, etc.)
   - View plugin details including ratings, install count, description
   - Install plugins with one click
   - Modal view for detailed plugin information

2. My Plugins (/plugins/my-plugins):
   - View all installed plugins
   - Manage plugin activation status
   - Update plugins when new versions available
   - Rate and review installed plugins
   - Uninstall plugins with confirmation
   - Links to create custom plugins and browse marketplace

Additional changes:
- Added plugin routes to App.tsx with owner/manager access control
- Updated HelpPluginDocs.tsx with navigation callout boxes
- Added TypeScript interfaces for PluginTemplate and PluginInstallation
- Both pages feature full dark mode support
- Professional UI with Tailwind CSS styling
- React Query integration for data fetching

The pages are accessible from the Plugins dropdown menu in the sidebar.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/types.ts

@@ -301,4 +301,38 @@ export interface OAuthProviderCredential {
 export interface BusinessOAuthCredentialsResponse {
   credentials: Record<string, OAuthProviderCredential>;
   useCustomCredentials: boolean;
+}
+
+// --- Plugin Types ---
+
+export type PluginCategory = 'EMAIL' | 'REPORTS' | 'CUSTOMER' | 'BOOKING' | 'INTEGRATION' | 'AUTOMATION' | 'OTHER';
+
+export interface PluginTemplate {
+  id: string;
+  name: string;
+  description: string;
+  category: PluginCategory;
+  version: string;
+  author: string;
+  rating: number;
+  ratingCount: number;
+  installCount: number;
+  isVerified: boolean;
+  isFeatured: boolean;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface PluginInstallation {
+  id: string;
+  template: string;
+  templateName: string;
+  templateDescription: string;
+  category: PluginCategory;
+  version: string;
+  isActive: boolean;
+  installedAt: string;
+  hasUpdate: boolean;
+  rating?: number;
+  review?: string;
 }