fix(spotify): make Start Spotify on TV idempotent

[postigodev]

Summary

Start Spotify on TV can currently pause playback when Spotify is already playing on the selected TV target.

Current behavior

spotify::start_on_tv() prepares the Fire TV session and then calls toggle_on_tv().

toggle_on_tv() intentionally toggles playback: when the selected TV is already the active playback device and playback is running, it calls pause_playback().

That means an action named Start Spotify on TV can produce Paused Spotify on ....

Expected behavior

Start Spotify on TV should be idempotent with respect to an already-running TV session:

• connect/wake the Fire TV as needed
• launch Spotify on Fire TV as needed
• ensure playback is routed to the selected TV target
• resume/start playback when necessary
• leave playback running when it is already running on that target

The explicit play/pause action can keep toggle semantics.

Acceptance criteria

• start_on_tv() no longer uses a toggle operation whose success path can pause playback
• invoking Start while playback is already active on the target does not pause it
• invoking Start while playback is elsewhere routes/resumes it on the target
• existing explicit playback-toggle behavior remains unchanged
• add focused regression coverage for the already-playing-on-target case

Likely files

• crates/core/src/spotify/mod.rs
• associated Spotify tests