Android: ship the achievement sounds

The unlock / message / leaderboard-submit sounds were caught by the blanket
*.wav ignore, so the assets folder shipped empty from a clean clone even though
local builds had the files on disk. Add them and un-ignore that folder so future
sounds aren't dropped the same way.

.gitignore

@@ -129,3 +129,6 @@ CMakeSettings.json
 /ci-artifacts/
 /out/
 /.cache/
+
+# Achievement sounds are shipped assets, not build output — keep them tracked
+!platforms/android/app/src/main/assets/resources/sounds/**/*.wav