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/bot/instance.test.ts

@@ -6,6 +6,7 @@ import type { SpotifyController } from "../music/spotify/controller.js";
 import type { SpotifyOAuth } from "../music/spotify/spotify-oauth.js";
 import type { MusicProvider } from "../music/provider.js";
 import type { BotDatabase } from "../data/database.js";
+import { createDatabase } from "../data/database.js";
 import type { AvatarStore } from "../data/avatars.js";
 import type { BotConfig } from "../data/config.js";
 
@@ -832,6 +833,9 @@ describe("BotInstance — spotifyOAuth threading to the controller factory (C3.1
     const database = {
       getProfileConfig: () => ({}),
       getCustomAvatarPath: () => null,
+      getPlayerSettings: () => ({ volume: 75, playMode: "seq" }),
+      saveVolume: () => {},
+      savePlayMode: () => {},
     } as unknown as BotDatabase;
     const options: BotInstanceOptions = {
       id: "bot-oauth-test",
@@ -912,6 +916,136 @@ describe("spotifyPortsForBotId — per-bot go-librespot ports (Fix 3)", () => {
   });
 });
 
+// --- Persisting volume + play mode across restarts (#125) ------------------
+const cmdVol = (BotInstance.prototype as any).cmdVol as (this: unknown, cmd: any) => string;
+const cmdMode = (BotInstance.prototype as any).cmdMode as (this: unknown, cmd: any) => string;
+
+describe("BotInstance.cmdVol — persistence (#125)", () => {
+  function makeVolCtx() {
+    let stored = 75;
+    return {
+      id: "bot1",
+      player: {
+        setVolume: vi.fn((v: number) => { stored = v; }),
+        getVolume: vi.fn(() => stored),
+      },
+      database: { saveVolume: vi.fn() },
+      logger: { warn: vi.fn() },
+      emit: vi.fn(),
+      // The real private persist helper lives on the prototype; wire it so the
+      // test exercises the shipped persistence path end-to-end.
+      persistVolume: (BotInstance.prototype as any).persistVolume,
+    } as any;
+  }
+
+  it("saves the new volume via database.saveVolume (covers chat !vol AND the REST endpoint)", () => {
+    const ctx = makeVolCtx();
+    const res = cmdVol.call(ctx, { args: "40" });
+    expect(res).toBe("Volume set to 40%");
+    expect(ctx.player.setVolume).toHaveBeenCalledWith(40);
+    expect(ctx.database.saveVolume).toHaveBeenCalledWith("bot1", 40);
+    expect(ctx.emit).toHaveBeenCalledWith("stateChange");
+  });
+
+  it("does not persist an out-of-range volume", () => {
+    const ctx = makeVolCtx();
+    const res = cmdVol.call(ctx, { args: "999" });
+    expect(res).toBe("Usage: !vol <0-100>");
+    expect(ctx.player.setVolume).not.toHaveBeenCalled();
+    expect(ctx.database.saveVolume).not.toHaveBeenCalled();
+  });
+
+  it("swallows a database error so the volume change still succeeds", () => {
+    const ctx = makeVolCtx();
+    ctx.database.saveVolume = vi.fn(() => { throw new Error("disk full"); });
+    const res = cmdVol.call(ctx, { args: "50" });
+    expect(res).toBe("Volume set to 50%");
+    expect(ctx.player.setVolume).toHaveBeenCalledWith(50);
+    expect(ctx.logger.warn).toHaveBeenCalled();
+  });
+});
+
+describe("BotInstance.cmdMode — persistence (#125)", () => {
+  function makeModeCtx() {
+    let mode = "seq";
+    return {
+      id: "bot1",
+      queue: {
+        setMode: vi.fn((m: string) => { mode = m; }),
+        getMode: vi.fn(() => mode),
+      },
+      database: { savePlayMode: vi.fn() },
+      logger: { warn: vi.fn() },
+      emit: vi.fn(),
+      persistPlayMode: (BotInstance.prototype as any).persistPlayMode,
+    } as any;
+  }
+
+  it("saves the new play mode via database.savePlayMode", () => {
+    const ctx = makeModeCtx();
+    const res = cmdMode.call(ctx, { args: "rloop" });
+    expect(res).toBe("Play mode set to: rloop");
+    expect(ctx.queue.setMode).toHaveBeenCalledWith("rloop");
+    expect(ctx.database.savePlayMode).toHaveBeenCalledWith("bot1", "rloop");
+    expect(ctx.emit).toHaveBeenCalledWith("stateChange");
+  });
+
+  it("does not persist an unknown mode", () => {
+    const ctx = makeModeCtx();
+    const res = cmdMode.call(ctx, { args: "bogus" });
+    expect(res).toBe("Usage: !mode <seq|loop|random|rloop>");
+    expect(ctx.queue.setMode).not.toHaveBeenCalled();
+    expect(ctx.database.savePlayMode).not.toHaveBeenCalled();
+  });
+});
+
+describe("BotInstance — restores persisted player settings on construction (#125)", () => {
+  const provider = { platform: "netease" } as unknown as MusicProvider;
+  function makeOptions(id: string, database: BotDatabase): BotInstanceOptions {
+    const logger: any = { info() {}, warn() {}, error() {}, debug() {}, child() { return logger; } };
+    return {
+      id,
+      name: "RestoreBot",
+      tsOptions: { host: "localhost", port: 9987, queryPort: 10011, nickname: "RestoreBot" } as any,
+      neteaseProvider: provider,
+      qqProvider: provider,
+      bilibiliProvider: provider,
+      youtubeProvider: provider,
+      database,
+      config: { spotify: {} } as unknown as BotConfig,
+      logger,
+      avatarStore: { read: () => null } as unknown as AvatarStore,
+      spotifyControllerFactory: () => ({ on: () => {} } as unknown as SpotifyController),
+    };
+  }
+
+  it("applies the saved volume + play mode from the database", () => {
+    const db = createDatabase(":memory:");
+    db.saveBotInstance({
+      id: "bot-restore", name: "B", serverAddress: "x", serverPort: 9987, nickname: "n",
+      defaultChannel: "", channelId: "", channelPassword: "", autoStart: false,
+      serverProtocol: "", ts6ApiKey: "", serverPassword: "",
+    });
+    db.saveVolume("bot-restore", 33);
+    db.savePlayMode("bot-restore", "loop");
+
+    const bot = new BotInstance(makeOptions("bot-restore", db));
+    const status = bot.getStatus();
+    expect(status.volume).toBe(33);
+    expect(status.playMode).toBe("loop");
+    db.close();
+  });
+
+  it("falls back to defaults for a bot with no saved settings", () => {
+    const db = createDatabase(":memory:");
+    const bot = new BotInstance(makeOptions("brand-new", db));
+    const status = bot.getStatus();
+    expect(status.volume).toBe(75);
+    expect(status.playMode).toBe("seq");
+    db.close();
+  });
+});
+
 describe("BotInstance.handleTextMessage — response chunking (#116)", () => {
   it("splits a long command response into multiple sends, each under the byte cap", async () => {
     const ctx = makeGateCtx({ adminGroups: [] });