feat(backend): Implement DexScreener connector (Story 1.1)

Core Implementation:
- Add DexScreenerConnector class with public API integration
- Implement token pair data fetching and indexing
- Add API routes: add, delete, test endpoints
- Register connector in task indexers and Celery tasks
- Add DEXSCREENER_CONNECTOR enum to database models

Features:
- Support up to 50 tokens per connector
- Track prices, volume, liquidity across multiple DEXs
- EVM and Solana address validation
- Periodic sync support
- No API key required (public DexScreener API)

API Endpoints:
- POST /api/v1/connectors/dexscreener/add
- DELETE /api/v1/connectors/dexscreener
- GET /api/v1/connectors/dexscreener/test

All endpoints require JWT authentication ✅
Integration tests passing ✅
Ready for production deployment ✅

surfsense_backend/app/routes/__init__.py

@@ -25,6 +25,7 @@ from .jira_add_connector_route import router as jira_add_connector_router
 from .linear_add_connector_route import router as linear_add_connector_router
 from .logs_routes import router as logs_router
 from .luma_add_connector_route import router as luma_add_connector_router
+from .dexscreener_add_connector_route import router as dexscreener_add_connector_router
 from .new_chat_routes import router as new_chat_router
 from .new_llm_config_routes import router as new_llm_config_router
 from .notes_routes import router as notes_router
@@ -56,6 +57,7 @@ router.include_router(google_drive_add_connector_router)
 router.include_router(airtable_add_connector_router)
 router.include_router(linear_add_connector_router)
 router.include_router(luma_add_connector_router)
+router.include_router(dexscreener_add_connector_router)
 router.include_router(notion_add_connector_router)
 router.include_router(slack_add_connector_router)
 router.include_router(teams_add_connector_router)