Refactor TTS segment identification to support canonical segment keys, decoupling segment IDs from locator and index for more robust deduplication and handoff. Add `segmentKey` to segment types, manifest, and ensure route. Implement natural sorting for EPUB CFI locations and segment locators using new comparison utilities. Update sidebar and manifest helpers to use locator-aware sorting. Add foundational modules for EPUB word highlighting, TTS segment planning, and EPUB handoff logic. Expand types and tests to cover new canonical segment and locator behaviors.
BREAKING CHANGE: TTS segment IDs now support canonical segment keys; APIs and manifest consumers must handle `segmentKey` and updated locator comparison logic.
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.
