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/interfaces/index.ts

@@ -6,6 +6,7 @@
 
 export type { ISTTProvider } from "./stt-provider.interface";
 export type { ITTSProvider } from "./tts-provider.interface";
+export { SPEECH_TIERS, AUDIO_FORMATS } from "./speech-types";
 export type {
   SpeechTier,
   AudioFormat,

apps/api/src/speech/interfaces/speech-types.ts

@@ -12,19 +12,21 @@
 // ==========================================
 
 /**
- * TTS provider tier.
+ * Canonical array of TTS provider tiers.
  * Determines which TTS engine is used for synthesis.
  *
  * - default: Primary TTS engine (e.g., Kokoro)
  * - premium: Higher quality TTS engine (e.g., Chatterbox)
  * - fallback: Backup TTS engine (e.g., Piper/OpenedAI)
  */
-export type SpeechTier = "default" | "premium" | "fallback";
+export const SPEECH_TIERS = ["default", "premium", "fallback"] as const;
+export type SpeechTier = (typeof SPEECH_TIERS)[number];
 
 /**
- * Audio output format for TTS synthesis.
+ * Canonical array of audio output formats for TTS synthesis.
  */
-export type AudioFormat = "mp3" | "wav" | "opus" | "flac" | "aac" | "pcm";
+export const AUDIO_FORMATS = ["mp3", "wav", "opus", "flac", "aac", "pcm"] as const;
+export type AudioFormat = (typeof AUDIO_FORMATS)[number];
 
 // ==========================================
 // STT Types

apps/api/src/speech/interfaces/stt-provider.interface.ts

@@ -16,7 +16,7 @@ import type { TranscribeOptions, TranscriptionResult } from "./speech-types";
  *
  * @example
  * ```typescript
- * class SpeachesProvider implements ISTTProvider {
+ * class SpeachesSttProvider implements ISTTProvider {
  *   readonly name = "speaches";
  *
  *   async transcribe(audio: Buffer, options?: TranscribeOptions): Promise<TranscriptionResult> {