feat(android): persist client_id for play-event reporting

Adds a stable client_id column to auth_session for the upcoming
PlayEventsReporter. Lazily generated on first read by the reporter;
deliberately survives sign-out since it's a device install identity,
not a session value. DB version bump 3→4 (destructive migration per
the pre-release policy).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/minstrel/auth/AuthStore.kt

@@ -43,6 +43,9 @@ class AuthStore @Inject constructor(
     private val themeModeState = MutableStateFlow<String?>(null)
     val themeMode: StateFlow<String?> = themeModeState.asStateFlow()
 
+    private val clientIdState = MutableStateFlow<String?>(null)
+    val clientId: StateFlow<String?> = clientIdState.asStateFlow()
+
     init {
         scope.launch {
             dao.observe().collect { row ->
@@ -50,6 +53,7 @@ class AuthStore @Inject constructor(
                 baseUrlState.value = row?.baseUrl ?: DEFAULT_BASE_URL
                 userJsonState.value = row?.userJson
                 themeModeState.value = row?.themeMode
+                clientIdState.value = row?.clientId
             }
         }
     }
@@ -74,6 +78,11 @@ class AuthStore @Inject constructor(
         scope.launch { persistThemeMode(value) }
     }
 
+    fun setClientId(value: String?) {
+        clientIdState.value = value
+        scope.launch { persistClientId(value) }
+    }
+
     private suspend fun persistCookie(value: String?) {
         if (dao.get() == null) {
             dao.upsert(currentEntity().copy(sessionCookie = value))
@@ -106,12 +115,21 @@ class AuthStore @Inject constructor(
         }
     }
 
+    private suspend fun persistClientId(value: String?) {
+        if (dao.get() == null) {
+            dao.upsert(currentEntity().copy(clientId = value))
+        } else {
+            dao.setClientId(value)
+        }
+    }
+
     private fun currentEntity(): AuthSessionEntity = AuthSessionEntity(
         id = ROW_ID,
         sessionCookie = sessionCookieState.value,
         baseUrl = baseUrlState.value,
         userJson = userJsonState.value,
         themeMode = themeModeState.value,
+        clientId = clientIdState.value,
     )
 
     companion object {

android/app/src/main/java/com/fabledsword/minstrel/cache/db/AppDatabase.kt

@@ -59,7 +59,7 @@ import com.fabledsword.minstrel.cache.db.entities.SyncMetadataEntity
         CachedHomeIndexEntity::class,
         AuthSessionEntity::class,
     ],
-    version = 3,
+    version = 4,
     exportSchema = true,
 )
 @TypeConverters(MinstrelTypeConverters::class)

android/app/src/main/java/com/fabledsword/minstrel/cache/db/dao/AuthSessionDao.kt

@@ -34,4 +34,8 @@ interface AuthSessionDao {
     /** Partial update: change only the theme override ("light"/"dark"/null=system). */
     @Query("UPDATE auth_session SET themeMode = :themeMode WHERE id = 0")
     suspend fun setThemeMode(themeMode: String?)
+
+    /** Partial update: change only the stable client install id. */
+    @Query("UPDATE auth_session SET clientId = :clientId WHERE id = 0")
+    suspend fun setClientId(clientId: String?)
 }

android/app/src/main/java/com/fabledsword/minstrel/cache/db/entities/AuthSessionEntity.kt

@@ -28,4 +28,5 @@ data class AuthSessionEntity(
     val baseUrl: String,
     val userJson: String? = null,
     val themeMode: String? = null,
+    val clientId: String? = null,
 )