Abstracted direct fetch calls across components and contexts into new functions within `src/lib/client.ts`. This provides a consistent and centralized interface for interacting with backend APIs.
- Introduced `src/lib/client.ts` to encapsulate API request logic.
- Standardized audio buffer types (`TTSAudioBuffer`, `TTSAudioBytes`) in `src/types/tts.ts`.
- Moved client-specific request types (`TTSRequestPayload`, `TTSRequestHeaders`, `TTSRetryOptions`) to `src/types/client.ts`.
- Updated API routes and consumer components/contexts to leverage the new client library functions and type definitions.
- Removed `src/utils/audio.ts` as its utility functions are now part of `src/lib/client.ts`.
- Introduce `/api/whisper` endpoint which uses `whisper.cpp` (via a `WHISPER_CPP_BIN` executable) and `ffmpeg` to generate word-level audio alignments from provided audio and text.
- Integrate word-level alignments into `TTSContext`, tracking the currently spoken word based on audio seek position and provided timestamps. Alignments are cached in-memory and fetched asynchronously.
- Add new configuration options (`pdfWordHighlightEnabled`, `epubWordHighlightEnabled`) to `ConfigContext` and `Dexie` for enabling/disabling the feature.
- Implement visual word highlighting in both `PDFViewer` and `EPUBViewer` by mapping TTS-aligned words to rendered text elements.
- Enhance `EPUBContext` and `PDFContext` with new `highlightWordIndex` and `clearWordHighlights` functions, utilizing fuzzy string matching (`cmpstr`) to robustly align spoken words with displayed text for accurate highlighting.
- Update `DocumentSettings` to include user-facing toggles for the new highlighting modes.
