feat(F2): integrate AES-256-CTR encryption into AdaptiveRecorder

After FFmpeg finishes writing, _stop_ffmpeg() now reads VIGILAR_ENCRYPTION_KEY
and encrypts the MP4 to .vge format via encrypt_file(), updating the returned
RecordingSegment to reflect the encrypted file path and size.

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

tests/unit/test_recorder_encryption.py

@@ -0,0 +1,10 @@
+"""Test encryption integration flag in recorder."""
+
+import os
+from vigilar.camera.recorder import AdaptiveRecorder
+
+
+def test_recorder_has_encryption_support():
+    """Verify recorder imports encryption module correctly."""
+    from vigilar.storage.encryption import encrypt_file
+    assert callable(encrypt_file)