refactor(tts): consolidate TTS services under lib/tts with stable entrypoint (#551)

* refactor(tts): move service module into domain folder

* refactor(tts): move summarization helpers into domain folder

* refactor(tts): add module entrypoint exports

* docs(tts): add module documentation

* refactor(web): route TTS imports through tts entrypoint

* docs(agents): map TTS module documentation

packages/web/server/lib/tts/index.js

@@ -0,0 +1,16 @@
+/**
+ * TTS Module Entry Point
+ *
+ * Public export surface for the Text-to-Speech domain module.
+ */
+
+export {
+  ttsService,
+  TTSService,
+  TTS_VOICES,
+} from './service.js';
+
+export {
+  summarizeText,
+  sanitizeForTTS,
+} from './summarization.js';