fix(playback): sync play/pause button with media keys

[mihaimetal]

Summary

• Keep the player play/pause icon in sync when OS media keys (e.g. macOS F8) toggle playback.
• On macOS, hardware media keys often pause/resume the WebKit <audio> element directly instead of going through the souvlaki media-control path, so sound changed but the store’s playing flag (and thus the button) did not.
• Mirror element play / pause events into the playback store.
• Briefly suppress that sync during intentional track-switch pauses so auto-advance still keeps playing: true.

Test plan

• Play a track, press F8 (media play/pause) — audio pauses and the player button switches to Play
• Press F8 again — audio resumes and the button switches to Pause
• In-app play/pause button and Space still work
• Skipping tracks still auto-resumes without the button flipping to Play mid-switch
• macOS release build smoke-tested

Notes

Independent of the WEB_REMIX / auth / packaging PRs; can merge on its own against main.