docs: Android comments say what the app does, not how it came to be (#6277)

Every flagged comment block in the Android app, its tests and its XML/TOML
config, rewritten with the cited issue in view: the constraint is kept, the
story behind it dropped, and issue, milestone, rule, phase and drift ids,
dates and operator quotes removed. "Mirrors the Flutter client's X"
pointers are gone; that client is no longer in the repo.

Comments that no longer matched the code, corrected:
- SyncController: a 410 resets the cursor and re-pulls; it never dropped
  the three local caches.
- PlayerFactory, PlayerModule, AudioCacheIndexEntity, CacheConfig,
  CacheSource: there is no eviction worker and no liked-track bucket;
  SimpleCache evicts by plain LRU over the rolling cap, and the liked cap
  is stored but unenforced.
- CacheSettings, StorageCard: the prefetcher exists (AudioPrefetcher);
  pin-on-like still does not.
- LibraryApi, LibraryRepository, BrowseViewModel: the cache now carries
  the missing-file mark; the browse indexes stay server-backed for one
  source of grouping.
- OutputRoute: UPnP routes exist; only CAST and SONOS are reserved.
- PlayerFactory, RemotePlayerState, OutputPickerController: a failed
  transport command does not drop the UPnP route.
- LibraryScreen: History, Liked and Hidden are real tabs, not placeholders.
- AVTransportClient: the extend loop lives in SonosQueueLoader.
- "the operator" meaning the listener now says "the user".

Verified with a Kotlin lexer comparing every file's non-comment tokens
against HEAD: 394 files, 0 differences.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/gradle/libs.versions.toml

@@ -5,7 +5,7 @@
 #   - Kotlin 2.3.x: AGP 9's built-in Kotlin path; the older kotlin-android
 #     plugin can't cast AGP 9's ApplicationExtension to the removed
 #     BaseExtension, and KSP 1.x isn't compatible with built-in Kotlin
-#   - KSP 2.3.x (PR #2674, merged Oct 2025): adds AGP 9 built-in Kotlin
+#   - KSP 2.3.x: adds AGP 9 built-in Kotlin
 #     support, so we don't need the kotlin-android plugin at all
 agp = "9.0.1"
 kotlin = "2.3.21"