feat: persist volume, play mode and audio quality across restarts

Runtime playback settings were kept only in memory (AudioPlayer.volume,
PlayQueue.mode, each provider's quality field), so restarting the bot reset
them to defaults and users had to re-tune volume and quality every time (#125).

Persist and restore them via the repo's existing storage:
- Volume and play mode are per-bot, stored on new bot_instances columns
  (volume, play_mode) with a schema migration; restored when the instance is
  (re)built, written by cmdVol / cmdMode which every entry point (chat command,
  WebUI, REST) funnels through. Volume and mode are written independently so a
  transient !fm/!artist mode switch never overwrites the user's saved !mode.
- Per-provider audio quality is global (shared providers), stored in a new
  config.json `audioQuality` block; applied to the providers at startup and
  re-snapshotted on POST /api/music/quality.

Queue, current song, progress and FM/artist sessions stay ephemeral.

Adds tests for config sanitize/round-trip, DB player-settings + migration,
cmdVol/cmdMode persistence + construction-time restore, and quality persistence
through the REST endpoint. Documents the behavior in the README.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/data/database.ts

@@ -55,6 +55,26 @@ export const DEFAULT_PROFILE_CONFIG: ProfileConfig = {
   nowPlayingMsgEnabled: true,
 };
 
+/**
+ * Per-bot player settings persisted across restarts (#125): the playback volume
+ * and play mode. These reset to defaults on process restart when kept only in
+ * memory (AudioPlayer/PlayQueue), so they are stored on the bot_instances row —
+ * exactly like the per-bot profile flags — and restored when the bot is (re)built.
+ */
+export interface PlayerSettings {
+  /** 0-100. */
+  volume: number;
+  /** PlayMode string: "seq" | "loop" | "random" | "rloop". */
+  playMode: string;
+}
+
+const PLAY_MODES = new Set(["seq", "loop", "random", "rloop"]);
+
+export const DEFAULT_PLAYER_SETTINGS: PlayerSettings = {
+  volume: 75,
+  playMode: "seq",
+};
+
 export interface FavoritePlaylist {
   id: number;
   userId: string;
@@ -75,6 +95,9 @@ export interface BotDatabase {
   deleteBotInstance(id: string): boolean;
   getProfileConfig(botId: string): ProfileConfig;
   saveProfileConfig(botId: string, config: ProfileConfig): void;
+  getPlayerSettings(botId: string): PlayerSettings;
+  saveVolume(botId: string, volume: number): void;
+  savePlayMode(botId: string, playMode: string): void;
   getCustomAvatarPath(botId: string): string | null;
   setCustomAvatarPath(botId: string, path: string | null): void;
   addFavorite(userId: string, playlist: { platform: string; playlistId: string; name: string; coverUrl: string; songCount: number }): void;
@@ -119,6 +142,15 @@ function migrateSchema(db: Database.Database): void {
   if (!names.includes("custom_avatar_path")) {
     db.exec("ALTER TABLE bot_instances ADD COLUMN custom_avatar_path TEXT");
   }
+  // Per-bot persisted player settings (#125): volume + play mode. Defaults match
+  // AudioPlayer/PlayQueue's in-memory defaults so pre-existing rows keep behaving
+  // exactly as before until the user changes them.
+  if (!names.includes("volume")) {
+    db.exec("ALTER TABLE bot_instances ADD COLUMN volume INTEGER NOT NULL DEFAULT 75");
+  }
+  if (!names.includes("play_mode")) {
+    db.exec("ALTER TABLE bot_instances ADD COLUMN play_mode TEXT NOT NULL DEFAULT 'seq'");
+  }
 
   const userColumns = db.prepare("PRAGMA table_info(users)").all() as Array<{ name: string }>;
   const userColNames = userColumns.map((c) => c.name);
@@ -161,6 +193,8 @@ function initTables(db: Database.Database): void {
       serverProtocol TEXT NOT NULL DEFAULT '',
       ts6ApiKey TEXT NOT NULL DEFAULT '',
       serverPassword TEXT NOT NULL DEFAULT '',
+      volume INTEGER NOT NULL DEFAULT 75,
+      play_mode TEXT NOT NULL DEFAULT 'seq',
       identity TEXT
     );
 
@@ -321,6 +355,12 @@ export function createDatabase(dbPath: string): BotDatabase {
     WHERE id = @id
   `);
 
+  const selectPlayerSettings = db.prepare(
+    `SELECT volume, play_mode FROM bot_instances WHERE id = ?`,
+  );
+  const updateVolume = db.prepare(`UPDATE bot_instances SET volume = ? WHERE id = ?`);
+  const updatePlayMode = db.prepare(`UPDATE bot_instances SET play_mode = ? WHERE id = ?`);
+
   const selectCustomAvatar = db.prepare(`SELECT custom_avatar_path FROM bot_instances WHERE id = ?`);
   const updateCustomAvatar = db.prepare(`UPDATE bot_instances SET custom_avatar_path = ? WHERE id = ?`);
 
@@ -406,6 +446,36 @@ export function createDatabase(dbPath: string): BotDatabase {
       });
     },
 
+    getPlayerSettings(botId) {
+      const row = selectPlayerSettings.get(botId) as
+        | { volume: number | null; play_mode: string | null }
+        | undefined;
+      if (!row) return { ...DEFAULT_PLAYER_SETTINGS };
+      // Coerce/validate: clamp volume to 0-100 and fall back to defaults for any
+      // NULL / out-of-range / unknown value (a hand-edited DB must never feed a
+      // bad value into AudioPlayer.setVolume / PlayQueue.setMode).
+      const rawVol = typeof row.volume === "number" ? row.volume : DEFAULT_PLAYER_SETTINGS.volume;
+      const volume = Number.isFinite(rawVol)
+        ? Math.max(0, Math.min(100, Math.round(rawVol)))
+        : DEFAULT_PLAYER_SETTINGS.volume;
+      const playMode =
+        typeof row.play_mode === "string" && PLAY_MODES.has(row.play_mode)
+          ? row.play_mode
+          : DEFAULT_PLAYER_SETTINGS.playMode;
+      return { volume, playMode };
+    },
+
+    saveVolume(botId, volume) {
+      const clamped = Math.max(0, Math.min(100, Math.round(volume)));
+      updateVolume.run(clamped, botId);
+    },
+
+    savePlayMode(botId, playMode) {
+      // Persist only recognized modes so a bad value can never poison the row.
+      if (!PLAY_MODES.has(playMode)) return;
+      updatePlayMode.run(playMode, botId);
+    },
+
     getCustomAvatarPath(botId) {
       const row = selectCustomAvatar.get(botId) as { custom_avatar_path: string | null } | undefined;
       return row?.custom_avatar_path ?? null;