fix(db): add ondelete cascade to all FK constraints, fix multimodal flag persistence

- Add ondelete=CASCADE/SET NULL to all environment and translate FK constraints
- Add is_multimodal to GET /api/settings/consolidated response
- Fix toggleActive to not overwrite is_multimodal with false
- New SearchableMultiSelect component for dashboard search with multi-select
- Fix validation task page: task data unwrapping, date formatting, dashboard multi-select
- Fix infinite effect loop on dashboards page via queueMicrotask guard
- 3 new Alembic migrations (merge f0e9d8c7b6a5, translate b0c1d2e3f4a5)

backend/src/api/routes/settings.py

@@ -437,6 +437,7 @@ async def get_consolidated_settings(
                     "api_key": "********",
                     "default_model": p.default_model,
                     "is_active": p.is_active,
+                    "is_multimodal": bool(p.is_multimodal) if p.is_multimodal is not None else False,
                 }
                 for p in providers
             ]