Fix/plugin examples cleanup

[DJJones66]

🧩 Add Demo API Endpoint, Improve Plugin State Handling, and Backend Refactor

🔍 Overview

This PR introduces a range of backend and frontend updates to support better plugin state management, enable future plugin demos, and improve developer experience:

• ✅ New demo.py API endpoint with full CRUD support for demonstration plugins
• ✅ Improved initialization and reliability of PluginStateService through asynchronous readiness handling
• ✅ Raw SQL insertion logic added to create_setting_instance to bypass SQLAlchemy relationship issues
• ✅ Simplified dev setup instructions and clarified ROADMAP.md entry
• 🧼 Removed unused image assets to reduce repo clutter

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📦 Backend Changes

1. demo.py: New Demo Plugin Endpoint

• Created a FastAPI router for /demo/ routes.

• Includes endpoints:

  • GET /demo/items: Retrieve user-specific demo items
  • POST /demo/items: Create item
  • PUT /demo/items/{id}: Update item
  • DELETE /demo/items/{id}: Delete item
  • GET /demo/status: API and user stats
  • GET /demo/health: Health check

• Uses in-memory storage (for non-production use).

2. settings.py: Raw SQL Insertion

• Switched from ORM instance creation to direct SQL execution for SettingInstance.
• Bypasses SQLAlchemy relationship resolution issues when saving settings with page and user scope.
• Adds logic to resolve 'current' user_id to the actual user at runtime.

3. api.py

• Registered new router: demo.router

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🧠 Plugin State Enhancements

PluginStateService.ts

• Introduced ensureInitialized() method to await PageContextService availability.
• Prevents intermittent runtime errors where state would be accessed before context was ready.

PluginStateFactory.ts

• Initialization now runs asynchronously with error logging, improving robustness without blocking startup.

serviceBridge.ts

• Added safe fallback logic for the pluginState service lookup.

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🧪 How to Test

1. Run the backend and hit /api/v1/demo/health – should return 200 OK
2. Login and try /api/v1/demo/items to create/view your items
3. Validate plugin state still persists correctly across page reloads and devices
4. Verify new setting instances write correctly with user and page scope

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📝 Notes

• This PR introduces non-breaking changes.
• The new /demo endpoints are scaffold-only and safe for use in examples or testing.