feat: Add plugin configuration editing with template variable parsing

## Backend Changes:
- Enhanced PluginTemplate.save() to auto-parse template variables from plugin code
- Updated PluginInstallationSerializer to expose template metadata (description, category, version, author, logo, template_variables)
- Fixed template variable parser to handle nested {{ }} braces in default values
- Added brace-counting algorithm to properly extract variables with insertion codes
- Fixed explicit type parameter detection (textarea, text, email, etc.)
- Made scheduled_task optional on PluginInstallation model
- Added EventPlugin through model for event-plugin relationships
- Added Event.execute_plugins() method for plugin automation

## Frontend Changes:
- Created Tasks.tsx page for managing scheduled tasks
- Enhanced MyPlugins page with clickable plugin cards
- Added edit configuration modal with dynamic form generation
- Implemented escape sequence handling (convert \n, \', etc. for display)
- Added plugin logos to My Plugins page
- Updated type definitions for PluginInstallation interface
- Added insertion code documentation to Plugin Docs

## Plugin System:
- All platform plugins now have editable email templates with textarea support
- Template variables properly parsed with full default values
- Insertion codes ({{CUSTOMER_NAME}}, {{BUSINESS_NAME}}, etc.) documented
- Plugin logos displayed in marketplace and My Plugins

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

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

frontend/src/App.tsx

@@ -65,6 +65,7 @@ import HelpPluginDocs from './pages/HelpPluginDocs'; // Import Plugin documentat
 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 Tasks from './pages/Tasks'; // Import Tasks page for scheduled plugin executions
 import { Toaster } from 'react-hot-toast'; // Import Toaster for notifications
 
 const queryClient = new QueryClient({
@@ -536,6 +537,16 @@ const AppContent: React.FC = () => {
               )
             }
           />
+          <Route
+            path="/tasks"
+            element={
+              hasAccess(['owner', 'manager']) ? (
+                <Tasks />
+              ) : (
+                <Navigate to="/" />
+              )
+            }
+          />
           <Route path="/support" element={<PlatformSupport />} />
           <Route
             path="/customers"