feat: add connections dashboard with background health checks

- Add /connections page showing all integrations with online/offline status
- Add background health checker that polls Evotor API every 10 minutes
- Add is_online and last_checked_at fields to evotor_connections table
- Replace Evotor navbar link with unified Connections link
- Redirect connect/disconnect flows to /connections
- Add Alembic migration for new columns

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/config.py

@@ -11,6 +11,8 @@ class Settings(BaseSettings):
     EVOTOR_CLIENT_SECRET: str = ""
     EVOTOR_SCOPES: str = "store:read product:read"
 
+    HEALTH_CHECK_INTERVAL_SECONDS: int = 600
+
     # Docker compose vars (ignored in app, kept for env compatibility)
     DB_ROOT_PASSWORD: str = ""
     DB_NAME: str = ""