chore: ruff lint auto-fix — 9 errors fixed (import sorting, unused imports)

- I001: import block sorting in main.py, routes/__init__.py, companies.py, conftest.py, check_indexes.py
- F401: unused imports removed (asyncio, UTC, datetime, AsyncSession)
- 6 ASYNC240/230 warnings remain (os.path.exists in async, open() in test) — minor, non-blocking

app/routes/companies.py

@@ -75,12 +75,14 @@ async def export_companies(
     tenant_id = uuid.UUID(current_user["tenant_id"])
 
     if format == "csv":
-        from app.models.company import Company
-        from sqlalchemy import select as sa_select
-        from app.core.db import get_session_factory
         import csv
         import io
+
         from fastapi.responses import StreamingResponse
+        from sqlalchemy import select as sa_select
+
+        from app.core.db import get_session_factory
+        from app.models.company import Company
 
         async def generate_csv():
             """Async generator yielding CSV rows (streaming, not buffered).