feat: paginated reader sync, search crash fix, audio cache + unified auth

- Sync pagination measurement with rendered layout (page geometry, spacing, images, chapter extras)
- Improve split algorithm with getLineForVerticalPosition and widow/orphan handling
- Fix search crash from duplicate LazyColumn keys on empty guids
- Switch BookCard cover to fixed-height vertical variant
- Add ExoPlayer SimpleCache + CacheDataSource for streaming audio
- Unify AuthorizationInterceptor for player via PlaybackAuthProvider
- Bump version to 1.9.11 (27) and update AGENTS.md

app/build.gradle.kts

@@ -19,8 +19,8 @@ android {
         applicationId = "org.dueattendant149.bookshelf"
         minSdk = 31
         targetSdk = 36
-        versionCode = 14
-        versionName = "1.8.0"
+        versionCode = 27
+        versionName = "1.9.11"
 
         vectorDrawables {
             useSupportLibrary = true