fix(#388): address PR review findings — fix WebSocket/REST bugs, improve error handling, fix types and comments

Critical fixes:
- Fix FormData field name mismatch (audio -> file) to match backend FileInterceptor
- Add /speech namespace to WebSocket connection URL
- Pass auth token in WebSocket handshake options
- Wrap audio.play() in try-catch for NotAllowedError and DOMException handling
- Replace bare catch block with named error parameter and descriptive message
- Add connect_error and disconnect event handlers to WebSocket
- Update JSDoc to accurately describe batch transcription (not real-time partial)

Important fixes:
- Emit transcription-error before disconnect in gateway auth failures
- Capture MediaRecorder error details and clean up media tracks on error
- Change TtsDefaultConfig.format type from string to AudioFormat
- Define canonical SPEECH_TIERS and AUDIO_FORMATS arrays as single source of truth
- Fix voice count from 54 to 53 in provider, AGENTS.md, and docs
- Fix inaccurate comments (Piper formats, tier prop, SpeachesProvider, TextValidationPipe)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/speech/providers/piper-tts.provider.ts

@@ -9,7 +9,7 @@
  * - OpenAI-compatible API via OpenedAI Speech server
  * - 100+ Piper voices across 40+ languages
  * - 6 standard OpenAI voice names mapped to Piper voices
- * - Output formats: mp3, wav, opus, flac, aac, pcm
+ * - Output formats: mp3, wav, opus, flac
  * - CPU-only, no GPU required
  * - GPL license (via OpenedAI Speech)
  *