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/tests/test_task_persistence.py

@@ -3,7 +3,6 @@
 # @SEMANTICS: test, task, persistence, unit_test
 # @PURPOSE: Unit tests for TaskPersistenceService.
 # @LAYER: Test
-# @COMPLEXITY: 5
 # @TEST_DATA: valid_task -> {"id": "test-uuid-1", "plugin_id": "backup", "status": "PENDING"}
 
 # [SECTION: IMPORTS]
@@ -23,7 +22,6 @@ from src.core.task_manager.models import Task, TaskStatus, LogEntry
 # [DEF:TestTaskPersistenceHelpers:Class]
 # @RELATION: BINDS_TO -> test_task_persistence
 # @PURPOSE: Test suite for TaskPersistenceService static helper methods.
-# @COMPLEXITY: 5
 class TestTaskPersistenceHelpers:
 
     # [DEF:test_json_load_if_needed_none:Function]
@@ -113,7 +111,6 @@ class TestTaskPersistenceHelpers:
 # [DEF:TestTaskPersistenceService:Class]
 # @RELATION: BINDS_TO -> test_task_persistence
 # @PURPOSE: Test suite for TaskPersistenceService CRUD operations.
-# @COMPLEXITY: 5
 # @TEST_DATA: valid_task -> {"id": "test-uuid-1", "plugin_id": "backup", "status": "PENDING"}
 class TestTaskPersistenceService: