Add completion_sound = "file" with [notifications].sound_file for Windows custom WAV completion sounds without changing the global Windows sound scheme.
The Windows path uses PlaySoundW asynchronously with no default fallback. Non-Windows file mode warns and no-ops, missing paths warn once, and setting a valid path resets the missing-path warning latch so later misconfiguration is visible again.
Fixes#2484
Reported by @LHqweasd
Harvested from PR #2512 by @cyq1017
Co-authored-by: cyq1017 <61975706+cyq1017@users.noreply.github.com>
Hunter B
91215d5f4f