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.test.ts

@@ -131,6 +131,92 @@ describe("database", () => {
     expect(botDb.deleteBotInstance("nonexistent")).toBe(false);
   });
 
+  it("persists and restores per-bot player settings (volume + play mode) (#125)", () => {
+    const inst = {
+      id: "bot-ps",
+      name: "B",
+      serverAddress: "x",
+      serverPort: 9987,
+      nickname: "n",
+      defaultChannel: "",
+      channelId: "",
+      channelPassword: "",
+      autoStart: false,
+      serverProtocol: "",
+      ts6ApiKey: "",
+      serverPassword: "",
+    };
+    botDb.saveBotInstance(inst);
+
+    // Fresh row → in-memory defaults.
+    expect(botDb.getPlayerSettings("bot-ps")).toEqual({ volume: 75, playMode: "seq" });
+
+    // Volume and play mode persist independently.
+    botDb.saveVolume("bot-ps", 42);
+    expect(botDb.getPlayerSettings("bot-ps")).toEqual({ volume: 42, playMode: "seq" });
+    botDb.savePlayMode("bot-ps", "rloop");
+    expect(botDb.getPlayerSettings("bot-ps")).toEqual({ volume: 42, playMode: "rloop" });
+
+    // A later saveBotInstance upsert (e.g. autoStart toggle) must NOT reset them.
+    botDb.saveBotInstance({ ...inst, autoStart: true });
+    expect(botDb.getPlayerSettings("bot-ps")).toEqual({ volume: 42, playMode: "rloop" });
+  });
+
+  it("defaults player settings for an unknown bot and validates inputs (#125)", () => {
+    // No row → defaults.
+    expect(botDb.getPlayerSettings("does-not-exist")).toEqual({ volume: 75, playMode: "seq" });
+
+    botDb.saveBotInstance({
+      id: "bot-v",
+      name: "B",
+      serverAddress: "x",
+      serverPort: 9987,
+      nickname: "n",
+      defaultChannel: "",
+      channelId: "",
+      channelPassword: "",
+      autoStart: false,
+      serverProtocol: "",
+      ts6ApiKey: "",
+      serverPassword: "",
+    });
+    // Out-of-range volume is clamped; an unknown play mode is ignored (not stored).
+    botDb.saveVolume("bot-v", 250);
+    expect(botDb.getPlayerSettings("bot-v").volume).toBe(100);
+    botDb.saveVolume("bot-v", -10);
+    expect(botDb.getPlayerSettings("bot-v").volume).toBe(0);
+    botDb.savePlayMode("bot-v", "bogus");
+    expect(botDb.getPlayerSettings("bot-v").playMode).toBe("seq");
+  });
+
+  it("migrates volume + play_mode columns onto a legacy bot_instances table (#125)", () => {
+    const dir = mkdtempSync(join(tmpdir(), "tsmb-mig-"));
+    const p = join(dir, "legacy.db");
+    // Build a minimal pre-#125 bot_instances table (no volume/play_mode columns).
+    const legacy = createDatabase(p);
+    legacy.db.exec("DROP TABLE bot_instances");
+    legacy.db.exec(`CREATE TABLE bot_instances (
+      id TEXT PRIMARY KEY, name TEXT NOT NULL, serverAddress TEXT NOT NULL,
+      serverPort INTEGER NOT NULL, nickname TEXT NOT NULL, defaultChannel TEXT NOT NULL,
+      channelId TEXT NOT NULL DEFAULT '', channelPassword TEXT NOT NULL,
+      autoStart INTEGER NOT NULL DEFAULT 0, serverProtocol TEXT NOT NULL DEFAULT '',
+      ts6ApiKey TEXT NOT NULL DEFAULT '', serverPassword TEXT NOT NULL DEFAULT '', identity TEXT
+    )`);
+    legacy.db
+      .prepare("INSERT INTO bot_instances (id, name, serverAddress, serverPort, nickname, defaultChannel, channelPassword) VALUES (?, 'B', 'x', 9987, 'n', '', '')")
+      .run("legacy-bot");
+    legacy.close();
+
+    // Reopen → migrateSchema adds the columns; the old row gets the defaults.
+    const reopened = createDatabase(p);
+    const cols = (reopened.db.prepare("PRAGMA table_info(bot_instances)").all() as Array<{ name: string }>).map((c) => c.name);
+    expect(cols).toContain("volume");
+    expect(cols).toContain("play_mode");
+    expect(reopened.getPlayerSettings("legacy-bot")).toEqual({ volume: 75, playMode: "seq" });
+    reopened.close();
+    rmSync(dir, { recursive: true, force: true });
+  });
+
   it("persists and clears customAvatarPath on a bot instance", () => {
     const inst = {
       id: "bot-1",