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

frontend/src/components/MissingMappingModal.svelte

@@ -26,7 +26,7 @@
 
   let selectedTargetUuid = $state("");
 
-  // [DEF:resolve:Function]
+  // #region resolve:Function [TYPE Function]
   // @PURPOSE: Resolves the missing mapping via callback prop.
   // @PRE: selectedTargetUuid must be set.
   // @POST: Parent callback receives mapping payload and modal closes.
@@ -39,9 +39,9 @@
     });
     show = false;
   }
-  // [/DEF:resolve:Function]
+  // #endregion resolve:Function
 
-  // [DEF:cancel:Function]
+  // #region cancel:Function [TYPE Function]
   // @PURPOSE: Cancels the mapping resolution modal.
   // @PRE: Modal is open.
   // @POST: Parent cancel callback is invoked and modal is hidden.
@@ -49,7 +49,7 @@
     oncancel();
     show = false;
   }
-  // [/DEF:cancel:Function]
+  // #endregion cancel:Function
 </script>
 
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