feat(#393): implement Kokoro-FastAPI TTS provider with voice catalog

Extract KokoroTtsProvider from factory into its own module with:
- Full voice catalog of 54 built-in voices across 8 languages
- Voice metadata parsing from ID prefix (language, gender, accent)
- Exported constants for supported formats and speed range
- Comprehensive unit tests (48 tests)
- Fix lint/type errors in chatterbox provider (Prettier + unsafe cast)

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

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

@@ -15,6 +15,8 @@
 
 import { Logger } from "@nestjs/common";
 import { BaseTTSProvider } from "./base-tts.provider";
+import { ChatterboxTTSProvider } from "./chatterbox-tts.provider";
+import { KokoroTtsProvider } from "./kokoro-tts.provider";
 import type { ITTSProvider } from "../interfaces/tts-provider.interface";
 import type { SpeechTier, AudioFormat } from "../interfaces/speech-types";
 import type { SpeechConfig } from "../speech.config";
@@ -23,28 +25,6 @@ import type { SpeechConfig } from "../speech.config";
 // Concrete provider classes
 // ==========================================
 
-/**
- * Kokoro TTS provider (default tier).
- * CPU-based, always available, Apache 2.0 license.
- */
-class KokoroProvider extends BaseTTSProvider {
-  readonly name = "kokoro";
-  readonly tier: SpeechTier = "default";
-}
-
-/**
- * Chatterbox TTS provider (premium tier).
- * GPU required, voice cloning capable, MIT license.
- */
-class ChatterboxProvider extends BaseTTSProvider {
-  readonly name = "chatterbox";
-  readonly tier: SpeechTier = "premium";
-
-  constructor(baseURL: string) {
-    super(baseURL, "default", "mp3");
-  }
-}
-
 /**
  * Piper TTS provider via OpenedAI Speech (fallback tier).
  * Ultra-lightweight CPU, GPL license.
@@ -78,7 +58,7 @@ export function createTTSProviders(config: SpeechConfig): Map<SpeechTier, ITTSPr
 
   // Default tier: Kokoro
   if (config.tts.default.enabled) {
-    const provider = new KokoroProvider(
+    const provider = new KokoroTtsProvider(
       config.tts.default.url,
       config.tts.default.voice,
       config.tts.default.format as AudioFormat
@@ -89,7 +69,7 @@ export function createTTSProviders(config: SpeechConfig): Map<SpeechTier, ITTSPr
 
   // Premium tier: Chatterbox
   if (config.tts.premium.enabled) {
-    const provider = new ChatterboxProvider(config.tts.premium.url);
+    const provider = new ChatterboxTTSProvider(config.tts.premium.url);
     providers.set("premium", provider);
     logger.log(`Registered premium TTS provider: chatterbox at ${config.tts.premium.url}`);
   }