Decompose monolithic wirePlaybackTracking() into single-responsibility modules:
- PanelState: per-panel playback state (phase, segments, buffer, quality)
- EventWiring: attaches hls.js + video element event listeners
- BufferMonitor: periodic buffer health check with timer lifecycle
- PanelRenderer: per-panel overlay rendering (phase, quality, segments)
- AggregateRenderer: global status bar aggregating all panel states
- PanelFactory: DOM panel creation + HLS/direct playback routing
Each module handles one concern: state tracking, event registration,
buffer monitoring, overlay rendering, aggregate rendering, or DOM creation.
Also fix: walk() dead code bug in m3u8DeepProbeFn where the string check
was unreachable behind the object-type guard.
