feat(i18n): inject user language into AI agent system prompts

- Add _language_instruction() to deep_agent.py, reads language from core memory
- Append language directive to all 4 run_* functions (task/project/checkpoint/note)
- Minor fixes: alembic env, route imports, test cleanup

tests/test_integrations.py

@@ -40,11 +40,9 @@ Coverage:
 
 from __future__ import annotations
 
-import asyncio
 import json
-import uuid
 from datetime import datetime, timezone
-from unittest.mock import AsyncMock, MagicMock, Mock, PropertyMock, patch
+from unittest.mock import AsyncMock, MagicMock, PropertyMock, patch
 
 import pytest