Remove legacy TTS segment manifest and audio endpoints in favor of new presigned and fallback audio URL approach. Update segment manifest structure to include `audioPresignUrl` and `audioFallbackUrl` fields, deprecating the previous `audioUrl`. Refactor segment ensure logic and TTS context to utilize the new playback source model. Add server utilities for generating presigned S3 URLs and introduce new API routes for presign and fallback audio retrieval. Clean up obsolete client API functions and types to reflect the new manifest format.
Introduce TTS segment support with new database tables and migrations for both Postgres and SQLite. Implement segment ensure, audio, and manifest API endpoints, segment storage in S3, and segment authorization logic. Update TTS context and client API to use segment-based synthesis and retrieval. Add server-side helpers for segment ID, settings hash, locator normalization, and audio probing. Extend user data cleanup and teardown logic to remove TTS segment objects. Add unit tests for segment helpers.
BREAKING CHANGE: TTS synthesis now uses segment-based storage and APIs; database migrations required.
