Add --record flag to capture live stream frames to video file

[Konstantysz]

Summary

• New --record <path.avi> CLI flag records raw frames from live stream to a MJPEG video file
• Recording is lazy-init on first frame (frame size unknown before first Grab)
• Recorded file can be replayed via --replay for offline FSM analysis and tuning
• No-op in replay mode and when flag is omitted

Usage

# Record live session
./sh3ds --hardware config/hardware.yaml --hunt-config config/hunts/xy_starter_sr_fennekin.yaml --record debug_session.avi

# Replay the recording for analysis
./sh3ds --hardware config/hardware.yaml --hunt-config config/hunts/xy_starter_sr_fennekin.yaml --replay debug_session.avi

Test plan

• All 173 tests pass (no regressions)