feat(android): port cached_playlists + cached_playlist_tracks (M8 4.2 slice 3)

Two related entities mirroring flutter_client/lib/cache/db.dart:
  - CachedPlaylists — one row per playlist; `systemVariant` is null for
    user playlists and "for_you" / "songs_like_artist" / etc. for
    system-generated mixes (used by the add-to-playlist sheet filter)
  - CachedPlaylistTracks — composite-PK join table, `position` carries
    ordering inside a playlist

DAO surfaces split user vs system playlists at the query layer so
ViewModels don't have to filter — observeUserPlaylists/observeSystemPlaylists.
PlaylistTrackDao gets a deleteByPlaylist for the replace-all pattern
after a sync delta lands.

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

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

@@ -6,11 +6,15 @@ import androidx.room.TypeConverters
 import com.fabledsword.minstrel.cache.db.dao.CachedAlbumDao
 import com.fabledsword.minstrel.cache.db.dao.CachedArtistDao
 import com.fabledsword.minstrel.cache.db.dao.CachedLikeDao
+import com.fabledsword.minstrel.cache.db.dao.CachedPlaylistDao
+import com.fabledsword.minstrel.cache.db.dao.CachedPlaylistTrackDao
 import com.fabledsword.minstrel.cache.db.dao.CachedTrackDao
 import com.fabledsword.minstrel.cache.db.dao.SyncMetadataDao
 import com.fabledsword.minstrel.cache.db.entities.CachedAlbumEntity
 import com.fabledsword.minstrel.cache.db.entities.CachedArtistEntity
 import com.fabledsword.minstrel.cache.db.entities.CachedLikeEntity
+import com.fabledsword.minstrel.cache.db.entities.CachedPlaylistEntity
+import com.fabledsword.minstrel.cache.db.entities.CachedPlaylistTrackEntity
 import com.fabledsword.minstrel.cache.db.entities.CachedTrackEntity
 import com.fabledsword.minstrel.cache.db.entities.SyncMetadataEntity
 
@@ -34,6 +38,8 @@ import com.fabledsword.minstrel.cache.db.entities.SyncMetadataEntity
         CachedAlbumEntity::class,
         CachedTrackEntity::class,
         CachedLikeEntity::class,
+        CachedPlaylistEntity::class,
+        CachedPlaylistTrackEntity::class,
     ],
     version = 1,
     exportSchema = true,
@@ -45,4 +51,6 @@ abstract class AppDatabase : RoomDatabase() {
     abstract fun cachedAlbumDao(): CachedAlbumDao
     abstract fun cachedTrackDao(): CachedTrackDao
     abstract fun cachedLikeDao(): CachedLikeDao
+    abstract fun cachedPlaylistDao(): CachedPlaylistDao
+    abstract fun cachedPlaylistTrackDao(): CachedPlaylistTrackDao
 }

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

@@ -0,0 +1,38 @@
+package com.fabledsword.minstrel.cache.db.dao
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.OnConflictStrategy
+import androidx.room.Query
+import com.fabledsword.minstrel.cache.db.entities.CachedPlaylistEntity
+import kotlinx.coroutines.flow.Flow
+
+@Dao
+interface CachedPlaylistDao {
+    /** All playlists, user + system, sorted by name. */
+    @Query("SELECT * FROM cached_playlists ORDER BY name COLLATE NOCASE ASC")
+    fun observeAll(): Flow<List<CachedPlaylistEntity>>
+
+    /** User playlists only (systemVariant IS NULL) — for the add-to-playlist sheet. */
+    @Query(
+        "SELECT * FROM cached_playlists " +
+            "WHERE systemVariant IS NULL ORDER BY name COLLATE NOCASE ASC",
+    )
+    fun observeUserPlaylists(): Flow<List<CachedPlaylistEntity>>
+
+    /** System playlists for the home screen. */
+    @Query(
+        "SELECT * FROM cached_playlists " +
+            "WHERE systemVariant IS NOT NULL ORDER BY name COLLATE NOCASE ASC",
+    )
+    fun observeSystemPlaylists(): Flow<List<CachedPlaylistEntity>>
+
+    @Query("SELECT * FROM cached_playlists WHERE id = :id")
+    suspend fun getById(id: String): CachedPlaylistEntity?
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun upsertAll(rows: List<CachedPlaylistEntity>)
+
+    @Query("DELETE FROM cached_playlists WHERE id IN (:ids)")
+    suspend fun deleteByIds(ids: List<String>)
+}

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

@@ -0,0 +1,36 @@
+package com.fabledsword.minstrel.cache.db.dao
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.OnConflictStrategy
+import androidx.room.Query
+import com.fabledsword.minstrel.cache.db.entities.CachedPlaylistTrackEntity
+import kotlinx.coroutines.flow.Flow
+
+@Dao
+interface CachedPlaylistTrackDao {
+    @Query(
+        "SELECT * FROM cached_playlist_tracks " +
+            "WHERE playlistId = :playlistId ORDER BY position ASC",
+    )
+    fun observeByPlaylist(playlistId: String): Flow<List<CachedPlaylistTrackEntity>>
+
+    @Query(
+        "SELECT * FROM cached_playlist_tracks " +
+            "WHERE playlistId = :playlistId ORDER BY position ASC",
+    )
+    suspend fun getByPlaylist(playlistId: String): List<CachedPlaylistTrackEntity>
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun upsertAll(rows: List<CachedPlaylistTrackEntity>)
+
+    /** Replace-all pattern for a playlist; called after a sync delta lands. */
+    @Query("DELETE FROM cached_playlist_tracks WHERE playlistId = :playlistId")
+    suspend fun deleteByPlaylist(playlistId: String)
+
+    @Query(
+        "DELETE FROM cached_playlist_tracks " +
+            "WHERE playlistId = :playlistId AND trackId IN (:trackIds)",
+    )
+    suspend fun deleteTracksFromPlaylist(playlistId: String, trackIds: List<String>)
+}

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

@@ -0,0 +1,29 @@
+package com.fabledsword.minstrel.cache.db.entities
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+import kotlinx.datetime.Clock
+import kotlinx.datetime.Instant
+
+/**
+ * Cache row for one playlist (user or system). Mirrors
+ * `flutter_client/lib/cache/db.dart`'s `CachedPlaylists` Drift table.
+ *
+ * `systemVariant` is null for user playlists and one of
+ * "for_you" / "songs_like_artist" / "discover" / "todays_mix" / etc.
+ * for system-generated mixes. Lets the add-to-playlist sheet filter
+ * system playlists locally without a REST round-trip.
+ */
+@Entity(tableName = "cached_playlists")
+data class CachedPlaylistEntity(
+    @PrimaryKey val id: String,
+    val userId: String,
+    val name: String,
+    val description: String = "",
+    val isPublic: Boolean = false,
+    val coverPath: String? = null,
+    val trackCount: Int = 0,
+    val durationSec: Int = 0,
+    val systemVariant: String? = null,
+    val fetchedAt: Instant = Clock.System.now(),
+)

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

@@ -0,0 +1,19 @@
+package com.fabledsword.minstrel.cache.db.entities
+
+import androidx.room.Entity
+
+/**
+ * Ordered membership of tracks within a playlist. Mirrors
+ * `flutter_client/lib/cache/db.dart`'s `CachedPlaylistTracks` Drift table.
+ * Composite PK so the same track can only appear once per playlist;
+ * `position` carries the ordering.
+ */
+@Entity(
+    tableName = "cached_playlist_tracks",
+    primaryKeys = ["playlistId", "trackId"],
+)
+data class CachedPlaylistTrackEntity(
+    val playlistId: String,
+    val trackId: String,
+    val position: Int = 0,
+)