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/App.tsx

@@ -63,6 +63,8 @@ import HelpTicketing from './pages/HelpTicketing'; // Import Help page for ticke
 import HelpApiDocs from './pages/HelpApiDocs'; // Import API documentation page
 import HelpPluginDocs from './pages/HelpPluginDocs'; // Import Plugin documentation page
 import PlatformSupport from './pages/PlatformSupport'; // Import Platform Support page (for businesses to contact SmoothSchedule)
+import PluginMarketplace from './pages/PluginMarketplace'; // Import Plugin Marketplace page
+import MyPlugins from './pages/MyPlugins'; // Import My Plugins page
 import { Toaster } from 'react-hot-toast'; // Import Toaster for notifications
 
 const queryClient = new QueryClient({
@@ -514,6 +516,26 @@ const AppContent: React.FC = () => {
           <Route path="/help/ticketing" element={<HelpTicketing />} />
           <Route path="/help/api" element={<HelpApiDocs />} />
           <Route path="/help/plugins" element={<HelpPluginDocs />} />
+          <Route
+            path="/plugins/marketplace"
+            element={
+              hasAccess(['owner', 'manager']) ? (
+                <PluginMarketplace />
+              ) : (
+                <Navigate to="/" />
+              )
+            }
+          />
+          <Route
+            path="/plugins/my-plugins"
+            element={
+              hasAccess(['owner', 'manager']) ? (
+                <MyPlugins />
+              ) : (
+                <Navigate to="/" />
+              )
+            }
+          />
           <Route path="/support" element={<PlatformSupport />} />
           <Route
             path="/customers"