Fusion P2 diagnostic r4 - audio and level-transition fixes

Fixes erroneous host DSP overload handling that cut off healthy sustained voices,
including level music and the C-stick horn. Keeps the audio worker serviced during
scene teardown so area loading can finish instead of waiting indefinitely. PC
panic messages now report the original error directly. Includes the intervening
native audio-lifetime, sequence-register, cave-save, pellet-initialization and
vertex-decoding fixes since r3.

The user confirmed successful level loading and corrected audio on this exact
native build on October 10, 2026. Two-PC connected startup was independently
verified. Focused sustained-renderer and transition regressions pass. This is
not full campaign or cave save/resume acceptance. Experimental diagnostics remain
on. Both players must use r4; extract into a fresh folder and retain your campaigns.

Third-party notices and dependency sources from r3 remain included. Each player
supplies their own legal game data. No assets, saves, crash dumps or credentials
are included.