Probes UNMASKED_RENDERER_WEBGL once per page via a throwaway WebGL context; defaults the lava subsystem off on a positive software-renderer match or total WebGL failure; releases the throwaway context via WEBGL_lose_context after reading the renderer string to avoid exhausting the browser's per-page context limit.
Adds CoerceTheaterMode() to WaveformVisualizerControlState; ToggleLava/ToggleWaveform
call it before NotifyChanged so all observers see consistent state in one Changed cycle.
Covers the dead-end escape route bug (Phase 20 review finding).
Toggle left of the lava popover hides release content so the visualizer fills
the surface; player bar grows to carry the playing release's cover, title, and
share. State on WaveformVisualizerControlState; pages and bar observe it.
daniel-c-harvey