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/media/ytdlp.test.ts

@@ -43,7 +43,8 @@ describe("createYtDlp", () => {
 
   it("reads direct audio URL", async () => {
     const proc = new FakeProcess();
-    const ytdlp = createYtDlp({ spawn: vi.fn(() => proc) });
+    const spawn = vi.fn(() => proc);
+    const ytdlp = createYtDlp({ spawn });
 
     const result = ytdlp.getDirectAudioUrl("https://youtu.be/video");
     proc.stdout.write("https://audio.example.com/stream\n");
@@ -51,6 +52,45 @@ describe("createYtDlp", () => {
     proc.emit("close", 0);
 
     await expect(result).resolves.toBe("https://audio.example.com/stream");
+    expect(spawn).toHaveBeenCalledWith(
+      "yt-dlp",
+      [
+        "https://youtu.be/video",
+        "--get-url",
+        "--format",
+        "bestaudio[protocol^=http]/bestaudio/best",
+        "--no-playlist",
+        "--no-warnings",
+        "--quiet",
+      ],
+      { stdio: ["ignore", "pipe", "pipe"] },
+    );
+  });
+
+  it("reads direct video URL", async () => {
+    const proc = new FakeProcess();
+    const spawn = vi.fn(() => proc);
+    const ytdlp = createYtDlp({ spawn });
+
+    const result = ytdlp.getDirectVideoUrl("https://youtu.be/video");
+    proc.stdout.write("https://video.example.com/stream\n");
+    proc.stdout.end();
+    proc.emit("close", 0);
+
+    await expect(result).resolves.toBe("https://video.example.com/stream");
+    expect(spawn).toHaveBeenCalledWith(
+      "yt-dlp",
+      [
+        "https://youtu.be/video",
+        "--get-url",
+        "--format",
+        "bestvideo[protocol^=http]+bestaudio[protocol^=http]/best[protocol^=http]/best",
+        "--no-playlist",
+        "--no-warnings",
+        "--quiet",
+      ],
+      { stdio: ["ignore", "pipe", "pipe"] },
+    );
   });
 
   it("rejects when yt-dlp exits non-zero", async () => {