Move `epub-word-highlight`, `tts-epub-handoff`, and `tts-epub-preload` from shared to client/epub to clarify their usage and improve bundling. Update all imports to use new client paths. Extend TTS and sidebar logic to support HTML document progress tracking and restoration, introducing a new location format for HTML and consistent handling for non-EPUB readers.
BREAKING CHANGE: EPUB TTS utilities relocated to `lib/client/epub`; update import paths. HTML progress persistence now uses a new format incompatible with previous versions.
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.
