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)

frontend/src/components/llm/ProviderConfig.svelte

@@ -246,7 +246,6 @@
         base_url: provider.base_url,
         default_model: provider.default_model,
         is_active: provider.is_active,
-        is_multimodal: Boolean(provider.is_multimodal),
       };
       await requestApi(`/llm/providers/${provider.id}`, "PUT", updatePayload);
     } catch (err) {