fix(voice): revert to prism-media@2.0.0-alpha.0 to fix production runtime errors

Critical production fix for voice recording failures.

Issue:
- Voice recording failing at runtime with "prism.opus.OpusHead is not a constructor"
- Downgrade to prism-media@1.3.5 broke voice recording (missing OggLogicalBitstream/OpusHead classes)
- Code was written for 2.0.0-alpha.0 API

Root Cause:
- prism-media@1.3.5 lacks OggLogicalBitstream and OpusHead classes
- prism-media@2.0.0-alpha.0 has these classes (code was originally written for this version)
- Downgrade to fix peer dependency warning broke working feature

Solution:
- Reverted to prism-media@2.0.0-alpha.0 (original working version)
- Removed @ts-expect-error comments (no longer needed)
- Accept harmless peer dependency warning with @discordjs/voice

Verification:
- TypeScript compilation: 0 errors
- pnpm install successful
- Both versions coexist (pnpm handles dual versions)

Files Modified (3 surgical edits, <15 lines each):
- package.json: Changed version from ^1.3.5 to 2.0.0-alpha.0
- types.ts: Removed @ts-expect-error comment (line 59)
- segment.ts: Removed 2 @ts-expect-error comments (lines 40, 42)

Impact: Voice recording will now work in production

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/discord-gateway/package.json

@@ -34,7 +34,7 @@
     "pg": "^8.21.0",
     "pino": "^9.6.0",
     "piscina": "^5.1.4",
-    "prism-media": "^1.3.5",
+    "prism-media": "2.0.0-alpha.0",
     "sharp": "^0.34.5",
     "tiktoken": "^1.0.22",
     "ws": "^8.20.1",