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/services/clean_release/test_compliance_task_integration.py

@@ -1,6 +1,5 @@
 # [DEF:TestComplianceTaskIntegration:Module]
 # @RELATION: BELONGS_TO -> SrcRoot
-# @COMPLEXITY: 5
 # @SEMANTICS: tests, clean-release, compliance, task-manager, integration
 # @PURPOSE: Verify clean release compliance runs execute through TaskManager lifecycle with observable success/failure outcomes.
 # @LAYER: Tests
@@ -144,7 +143,6 @@ class CleanReleaseCompliancePlugin:
 
 # [DEF:_PluginLoaderStub:Class]
 # @RELATION: BINDS_TO -> TestComplianceTaskIntegration
-# @COMPLEXITY: 2
 # @PURPOSE: Provide minimal plugin loader contract used by TaskManager in integration tests.
 # @INVARIANT: has_plugin/get_plugin only acknowledge the seeded compliance plugin id.
 class _PluginLoaderStub: