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/package.json

@@ -9,6 +9,7 @@
     "@stripe/connect-js": "^3.3.31",
     "@stripe/react-connect-js": "^3.3.31",
     "@tanstack/react-query": "^5.90.10",
+    "@types/react-syntax-highlighter": "^15.5.13",
     "axios": "^1.13.2",
     "date-fns": "^4.1.0",
     "i18next": "^25.6.3",
@@ -21,6 +22,7 @@
     "react-i18next": "^16.3.5",
     "react-phone-number-input": "^3.4.14",
     "react-router-dom": "^7.9.6",
+    "react-syntax-highlighter": "^16.1.0",
     "recharts": "^3.5.0"
   },
   "devDependencies": {