feat(gateway): restore Discord GoLive screenshare (dulu pernah ada, hilang saat split microservices)

User: 'dulu sharescreen juga bisa'. Terbukti: commit d50ce86 (Mei 2026)
punya src/media/screenShareController.ts + vendor @dank074/discord-video-stream,
hilang saat rombak monolith -> microservices. Interface ScreenShareController
masih ada di mediaTypes.ts tapi implementasinya tidak.

Restore:
- dep @dank074/discord-video-stream@6.0.0 (npm, dibangun untuk
  discord.js-selfbot-v13 — cocok dengan stack gateway)
- mediaSource.getDirectVideoUrl (yt-dlp --get-url bestvideo+bestaudio)
- screenShareController.ts (BARU): Streamer(client) + prepareStream H264
  720p30 + playStream go-live; owner check via discordPlayer
- media.handler: mode:'screen' di media:queue -> screen path; status
  expose activeMode; stop matiin screen
- FE: tombol Screen di MusicPlayer + hook useMediaQueue({url, mode})

Verifikasi: gateway tsc PASS, FE tsc PASS, biome 0 error, next build PASS.
Nix build pending (dep native @lng2004/node-datachannel butuh pnpm rebuild).

services/discord-gateway/package.json

@@ -28,12 +28,12 @@
     "test": "vitest run"
   },
   "dependencies": {
+    "@dank074/discord-video-stream": "6.0.0",
     "@discordjs/opus": "^0.10.0",
     "@discordjs/voice": "^0.19.2",
     "@snazzah/davey": "^0.1.11",
     "axios": "^1.16.1",
     "discord.js-selfbot-v13": "^3.7.1",
-    "@dank074/discord-video-stream": "latest",
     "dotenv": "^17.4.2",
     "drizzle-orm": "^0.45.2",
     "imghash": "^1.1.4",