Investigate how to reliably control `volume-track` via system hotkey

[paulpv]

Summary

Research how the player can respond to system-level or external hotkeys (e.g., keyboard media keys, Stream Deck) so common playback controls work even when the window is unfocused. Start with volume-track adjustments, then extend the findings to other core actions.

Tasks

• Audit current volume-track handling in the player.
• Research browser APIs or OS integration options for intercepting system media keys and Stream Deck shortcuts.
• Prototype a reliable approach for volume up/down that works while the app is backgrounded.
• Extend the same mechanism so external triggers can toggle Loop, toggle Shuffle/Random, cycle track ratings, and jump forward/back 5 seconds.
• Propose implementation approach or document limitations for each action.