v0.4.1

v0.4.1 - Desktop battery / idle pass

The desktop now wakes for nothing when idle: background producers (library
scans, covers, sibling scans, folder watch, update check, opens) wake the
frame loop themselves and the 250ms polling heartbeat is replaced by a pure
deadline scheduler for the three real timers (folder-watch debounce, spinner
grace, toast expiry) - background results also land instantly instead of up
to 250ms late. Minimizing parks the decode pool (0% CPU) and restores
seamlessly. Config saves are atomic (temp + rename), so a crash can no longer
truncate settings/positions. New Performance setting in the gear panel:
Auto / Battery saver / Balanced / Performance, applied live without reopening
the book - Auto runs full performance on AC and drops to Balanced on battery.