feat(01-03): move cuVSLAM backends into components/vio/cuvslam_backend.py

- Extract CuVSLAMVisualOdometry (Inertial) + CuVSLAMMonoDepthVisualOdometry
  (Mono-Depth) from core/vo.py into a dedicated cuVSLAM-bridge module.
- Preserve the optional 'try: import cuvslam / except ImportError' pattern
  at module top with the _CUVSLAM_AVAILABLE flag — verified False on x86 dev,
  True on Jetson (PATTERNS.md §6.5, §8.1).
- Both classes embed an ORBVisualOdometry instance for transparent dev/CI
  fallback; metric scale semantics preserved (scale_ambiguous=False).
- Scaffold components/vio/native/ as Phase-1 placeholder for future native
  SDK glue (PATTERNS.md §1.4); Phase 1 is intentionally empty.
- Append both classes to the components.vio barrel.

src/gps_denied/components/vio/__init__.py

@@ -20,10 +20,16 @@ from gps_denied.components.vio.orbslam_backend import (
     ORBVisualOdometry,
     SequentialVisualOdometry,
 )
+from gps_denied.components.vio.cuvslam_backend import (
+    CuVSLAMMonoDepthVisualOdometry,
+    CuVSLAMVisualOdometry,
+)
 
 __all__ = [
     "VisualOdometry",
     "ISequentialVisualOdometry",
     "ORBVisualOdometry",
     "SequentialVisualOdometry",
+    "CuVSLAMVisualOdometry",
+    "CuVSLAMMonoDepthVisualOdometry",
 ]