fix(lint): resolve all ruff E402/I001/F821 errors

- Move pytestmark after all imports in 35 test files (E402: not-at-top)
- Add TYPE_CHECKING guard for FlightProcessor in composition.py (F821)
- Sort import blocks in src/ and tests/ (I001 auto-fix via ruff --fix)
- ruff check src/ tests/ now exits 0 with no errors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_api_flights.py

@@ -3,9 +3,6 @@
 import json
 
 import pytest
-
-pytestmark = [pytest.mark.integration]
-
 from httpx import ASGITransport, AsyncClient
 from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 
@@ -13,6 +10,8 @@ from gps_denied.app import app
 from gps_denied.db.engine import get_session
 from gps_denied.db.models import Base
 
+pytestmark = [pytest.mark.integration]
+
 
 @pytest.fixture
 async def override_get_session():