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_schemas.py

@@ -3,9 +3,6 @@
 from datetime import datetime, timezone
 
 import pytest
-
-pytestmark = [pytest.mark.unit]
-
 from pydantic import ValidationError
 
 from gps_denied.config import get_settings
@@ -20,6 +17,8 @@ from gps_denied.schemas.flight import (
     Waypoint,
 )
 
+pytestmark = [pytest.mark.unit]
+
 # ── GPSPoint ──────────────────────────────────────────────────────────────
 
 @pytest.mark.ac("AC-6.3")