Serialize heavy PCM seeding through a dedicated queue with optional priority
for the current track. Emit waveform-updated once per completed seed, fix
Lucky Mix waveform refresh tokens, redact Subsonic URLs in logs, and align
hot-cache prefetch with the queued path.
Small fix for hot playback cache: eviction keeps current and next only;
prefetch up to five tracks when under cap, always fetch the immediate next;
grace for the previous current until debounce; run evict immediately on
MB or folder changes; re-read cap after download; optional Track.size;
live disk usage on Audio settings.