docs: update changelog

Author: Splode

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ### Bug Fixes
 
+- **Custom notification sounds not playing on Windows** — ADPCM-encoded WAV files (the default output of Windows Sound Recorder) failed to decode because the `symphonia-codec-adpcm` crate was not in the dependency tree. The app would silently fall back to the built-in sound while still displaying the custom filename in Settings. ADPCM decoding is now enabled by adding `symphonia-codec-adpcm` as a direct dependency.
+- **Custom sound file picker offered FLAC, which could never be decoded** — the file picker filter included `.flac` as a valid extension, but FLAC decoding was never compiled in. FLAC has been removed from the filter.
+- **Unsupported audio format selected silently reverted to default** — when a custom sound file was copied successfully but failed to decode (unsupported encoding), the app fell back to the default sound with no indication to the user. The file is now probed immediately after being copied; if decoding fails the file is discarded and an inline error message is shown below the relevant audio row in Settings → Notifications.
 - **Timer not restarting correctly after quickly starting the next round** — when a round completed and the user clicked Start before the engine's follow-up duration update arrived, the update (a `Reconfigure` command) would force the engine back to Idle, cancelling the freshly started timer. The follow-up is now sent as a lighter-weight `Prime` command that updates the stored duration in place without affecting the running phase. Contributed by [@SeanTong11](https://github.com/SeanTong11).
 - **Timer completing instantly when a stale duration update arrives mid-round** — in a rare race, the engine could receive a `Prime` command carrying a duration shorter than the already-elapsed time (e.g. if the round duration was shortened in settings while a timer was running). Without a guard this caused the timer to complete on the very next tick. The `Prime` handler now clamps the new duration to at least one tick beyond the current elapsed position so the timer always advances at least once before completing.