Improve gesture tracking responsiveness and stability

[NakaokaRei]

Summary

• move Vision recognition and preview conversion off the main actor with latest-frame backpressure
• normalize pinch detection by hand size and add EMA smoothing, hysteresis, confirmation frames, and missing-hand reset
• bound pointer movement, compensate for the mirrored camera preview, and prevent repeated sequence actions
• reuse the image context and configure capture for 720p at 30 fps
• add lightweight OSLog timing and dropped-frame diagnostics

Testing

• xcodebuild -project TrackpadAir.xcodeproj -scheme TrackpadAir -configuration Debug -derivedDataPath /tmp/TrackpadAir-derived test CODE_SIGNING_ALLOWED=NO
• 23 tests passed