fix(matrix-tts-bot): add API key authentication for mana-tts service

- Add TTS_API_KEY config option to configuration.ts
- Send X-API-Key header in TtsService requests
- Update docker-compose.macmini.yml with TTS_INTERNAL_API_KEY env var
- Update .env.example and CLAUDE.md documentation

The mana-tts service requires authentication, but the TTS bot was not
sending the required X-API-Key header, causing 401 errors.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.macmini.yml

@@ -973,6 +973,7 @@ services:
       MATRIX_ACCESS_TOKEN: ${MATRIX_TTS_BOT_TOKEN}
       MATRIX_ALLOWED_ROOMS: ${MATRIX_TTS_BOT_ROOMS:-}
       TTS_URL: http://host.docker.internal:3022
+      TTS_API_KEY: ${TTS_INTERNAL_API_KEY:-}
       DEFAULT_VOICE: af_heart
       DEFAULT_SPEED: 1.0
       MAX_TEXT_LENGTH: 500