fix(llm): add fetch-models endpoint, fix SQL Lab INSERT (client_id truncation, sync mode, target_column, timestamp normalization)

- Add POST /api/llm/providers/fetch-models route with LLMClient.fetch_models()
- Add target_column to TranslationJob model/schema/service/orchestrator
- Fix SQL Lab execute: truncate client_id to 11 chars (varchar(11))
- Switch SQL Lab to sync mode (runAsync: false) — no Celery workers
- Fix polling: unwrap nested result from Superset query API
- Fix ClickHouse timestamp: normalize float timestamps to YYYY-MM-DD

backend/src/core/database.py

@@ -484,6 +484,24 @@ def _ensure_translation_jobs_columns(bind_engine):
                 )
                 raise
 
+        if "target_database_id" not in existing_columns:
+            try:
+                with bind_engine.begin() as connection:
+                    connection.execute(
+                        text(
+                            "ALTER TABLE translation_jobs "
+                            "ADD COLUMN target_database_id VARCHAR"
+                        )
+                    )
+                logger.reflect(
+                    "Added target_database_id column to translation_jobs",
+                )
+            except Exception as migration_error:
+                logger.explore(
+                    "Failed to add target_database_id to translation_jobs",
+                    extra={"error": str(migration_error)},
+                )
+
 
 def _ensure_dataset_review_session_columns(bind_engine):
     with belief_scope("_ensure_dataset_review_session_columns"):