Fix ExoPlayer wrong-thread crash + recordSearch off Main (perf-audit pass-2) — vc=79

- PlaybackService: the pauseOnHeadphoneDisconnect settings-watcher collector
  ran on globalScope (Dispatchers.IO) and called setHandleAudioBecomingNoisy
  on the ExoPlayer, which is thread-affine to the Main thread it was built on
  → latent IllegalStateException('Player accessed on the wrong thread') that
  fires every service start (the StateFlow emits on first subscription). Run
  the collector on Dispatchers.Main (mirrors resumePollJob).
- SearchViewModel: recordSearch (json-encode + SharedPrefs write) was on Main;
  wrap in withContext(Dispatchers.IO).

Both adversarially verified in the multi-agent perf audit (pass 2).

strawApp/src/main/kotlin/com/sulkta/straw/feature/player/PlaybackService.kt

@@ -128,7 +128,13 @@ class PlaybackService : MediaSessionService() {
         // without requiring a service restart. The initial value was
         // baked in via the builder above — this picks up subsequent
         // flips.
-        settingsWatcherJob = StrawApp.globalScope.launch {
+        // MUST run on Main: globalScope is Dispatchers.IO, but ExoPlayer is
+        // thread-affine to the Main thread it was built on (onCreate), so
+        // touching it (setHandleAudioBecomingNoisy) off-Main throws
+        // "Player is accessed on the wrong thread" — and this hot StateFlow
+        // emits on first subscription, i.e. every service start. Mirrors
+        // resumePollJob below.
+        settingsWatcherJob = StrawApp.globalScope.launch(Dispatchers.Main) {
             Settings.get().pauseOnHeadphoneDisconnect.collect { handle ->
                 player.setHandleAudioBecomingNoisy(handle)
             }

strawApp/src/main/kotlin/com/sulkta/straw/feature/search/SearchViewModel.kt

@@ -237,7 +237,8 @@ class SearchViewModel : ViewModel() {
                 }
                 // Record AFTER the search succeeds so mistyped queries
                 // that error out don't pollute the recent-searches list.
-                runCatching { History.get().recordSearch(q) }
+                // Off Main — recordSearch json-encodes + writes SharedPrefs.
+                withContext(Dispatchers.IO) { runCatching { History.get().recordSearch(q) } }
                 if (Settings.get().cacheEnabled.value) {
                     withContext(Dispatchers.IO) {
                         // Re-check active state after the dispatcher