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/conftest.py

@@ -1,14 +1,5 @@
 """Shared test fixtures for GPS-denied-onboard test suite."""
 
-from unittest.mock import AsyncMock, MagicMock
-
-import numpy as np
-import pytest
-
-from gps_denied.core.coordinates import CoordinateTransformer
-from gps_denied.core.models import ModelManager
-from gps_denied.schemas import CameraParameters, GPSPoint
-
 # ---------------------------------------------------------------
 # Phase 2 / TEST-03: AC traceability plugin
 #
@@ -23,6 +14,14 @@ import json
 import re
 from collections import defaultdict
 from pathlib import Path
+from unittest.mock import AsyncMock, MagicMock
+
+import numpy as np
+import pytest
+
+from gps_denied.core.coordinates import CoordinateTransformer
+from gps_denied.core.models import ModelManager
+from gps_denied.schemas import CameraParameters, GPSPoint
 
 _AC_ID_RE = re.compile(r"^AC-(?:\d+\.\d+[a-z]?|NEW-\d+)$")