feat: simplify reader UI + remove unused code + speed up build
Reader UI simplification:
- loadHiddenTools: by default hide all tools except THEME, SLIDER, TOC, BOOKMARK, READING_MODE
- User sees only: font/theme controls, navigation slider, chapters, bookmarks, reading mode
Speed optimization:
- Removed old unused Episteme screens: HomeScreen, LibraryScreen, MainScreen, SettingsScreen, ProScreen, AppNavigation
- Removed old bookshelf UI: BookshelfLibraryScreen, BookshelfViewModel (replaced by new ui/ screens)
- TensorFlow deps kept (needed by debug ML source set)
- Material-icons-extended added for icon availability
':app:assembleOssDebug' passes, APK deployed.
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