refactor(audio): extract AutoEQ proxy commands into own module

Pull autoeq_entries + autoeq_fetch_profile out of audio/commands.rs
into audio/autoeq_commands.rs (~52 LOC). They proxy autoeq.app +
GitHub raw content via Rust to bypass WebView CORS — pure HTTP-fetch
flow with no playback state coupling, so they don't need to live next
to the playback orchestrator.

lib.rs invoke_handler updated to register them under
`audio::autoeq_commands::*`. audio/commands.rs: 1830 → 1784 LOC.

src-tauri/src/lib.rs

@@ -395,8 +395,8 @@ pub fn run() {
             audio::commands::audio_set_volume,
             audio::commands::audio_update_replay_gain,
             audio::commands::audio_set_eq,
-            audio::commands::autoeq_entries,
-            audio::commands::autoeq_fetch_profile,
+            audio::autoeq_commands::autoeq_entries,
+            audio::autoeq_commands::autoeq_fetch_profile,
             audio::commands::audio_preload,
             audio::commands::audio_play_radio,
             audio::preview::audio_preview_play,