feat: implement media echo fix and YouTube screenshare design

- Introduced a new `ScreenShareController` to manage YouTube screenshare functionality.
- Updated `DiscordPlayer` to track ownership of audio streams, preventing conflicts between music playback and screenshare.
- Added error handling for various states including voice connection checks and media busy states.
- Created unit tests for `ScreenShareController` and `DiscordPlayer` ownership rules to ensure correct functionality.
- Added documentation for the new media echo fix and screenshare design.

tests/recorder.test.ts

@@ -0,0 +1,49 @@
+import { EventEmitter } from "node:events";
+import { describe, expect, it, vi } from "vitest";
+
+const speaking = new EventEmitter();
+const subscribe = vi.fn();
+const joinVoiceChannel = vi.fn(() => ({
+  receiver: {
+    speaking,
+    subscriptions: new Map(),
+    subscribe,
+  },
+  on: vi.fn(),
+  destroy: vi.fn(),
+}));
+
+vi.mock("@discordjs/voice", async () => {
+  const actual =
+    await vi.importActual<typeof import("@discordjs/voice")>(
+      "@discordjs/voice",
+    );
+  return {
+    ...actual,
+    joinVoiceChannel,
+    entersState: vi.fn(async () => undefined),
+  };
+});
+
+describe("startRecording", () => {
+  it("does not subscribe to the bot user's own audio", async () => {
+    const { startRecording } = await import("../src/recorder");
+    const client = {
+      user: { id: "bot-user" },
+    };
+    const channel = {
+      id: "voice-channel",
+      name: "Voice",
+      guild: {
+        id: "guild",
+        voiceAdapterCreator: {},
+      },
+    };
+
+    await startRecording(client as never, channel as never);
+    speaking.emit("start", "bot-user");
+    await new Promise((resolve) => setImmediate(resolve));
+
+    expect(subscribe).not.toHaveBeenCalled();
+  });
+});