mod: Phase 1 - bring forward mod-exclusive files with ActivityManager migration

Brings ~55 mod-exclusive files to the upstream-based mod/master-resync branch:

Activities (migrated to new ActivityManager pattern):
- Clock/Time: SetTimeActivity, SetTimezoneOffsetActivity, NtpSyncActivity
- Dictionary: DictionaryDefinitionActivity, DictionarySuggestionsActivity,
  DictionaryWordSelectActivity, LookedUpWordsActivity
- Bookmark: EpubReaderBookmarkSelectionActivity
- Book management: BookManageMenuActivity, EndOfBookMenuActivity
- OPDS: OpdsServerListActivity, OpdsSettingsActivity
- Utility: DirectoryPickerActivity, NumericStepperActivity

Utilities (unchanged):
- BookManager, BookSettings, BookmarkStore, BootNtpSync
- Dictionary, LookupHistory, TimeSync, OpdsServerStore

Libraries: PlaceholderCover, TableData, ChapterXPathIndexer
Scripts: inject_mod_version, generate_book_icon, preview_placeholder_cover
Docs: KOReader sync XPath mapping

Migration changes:
- ActivityWithSubactivity -> Activity base class
- Callback constructors -> finish()/setResult() pattern
- enterNewActivity() -> startActivityForResult()
- Activity::RenderLock&& -> RenderLock&&

These files won't compile yet - they reference mod settings and I18n
strings that will be added in subsequent phases.

Made-with: Cursor

chat-summaries/2026-02-12_prerender-book-covers-summary.md

@@ -0,0 +1,39 @@
+# Prerender Book Covers/Thumbnails on First Open
+
+**Date:** 2026-02-12
+**Branch:** `mod/prerender-book-covers`
+
+## Task
+
+Implement todo item: "Process/render all covers/thumbs when opening book for first time" with a progress indicator so the reader doesn't appear frozen.
+
+## Changes Made
+
+### `src/components/UITheme.h`
+- Added `PRERENDER_THUMB_HEIGHTS[]` and `PRERENDER_THUMB_HEIGHTS_COUNT` constants (226, 400) representing all known theme `homeCoverHeight` values (Lyra and Base). This ensures thumbnails are pre-generated for all themes.
+
+### `src/activities/reader/EpubReaderActivity.cpp`
+- Added prerender block in `onEnter()` after `setupCacheDir()` and before `addBook()`.
+- Checks whether `cover.bmp`, `cover_crop.bmp`, `thumb_226.bmp`, and `thumb_400.bmp` exist.
+- If any are missing, shows "Preparing book..." popup with a progress bar that updates after each generation step.
+- On subsequent opens, all files already exist and the popup is skipped entirely.
+
+### `src/activities/reader/XtcReaderActivity.cpp`
+- Added same prerender pattern in `onEnter()`.
+- Generates `cover.bmp`, `thumb_226.bmp`, and `thumb_400.bmp` (XTC has no cropped cover variant).
+
+### `src/activities/reader/TxtReaderActivity.cpp`
+- Added prerender for `cover.bmp` only (TXT has no thumbnail support).
+- Shows "Preparing book..." popup if the cover needs generating.
+
+## Design Decisions
+
+- **Letterbox edge data not prerendered:** The sleep screen's letterbox gradient fill (`cover_edges.bin`) depends on runtime settings (crop mode, screen dimensions) and is already efficiently cached after first sleep. The expensive part (JPEG-to-BMP conversion) is what this change addresses.
+- **TXT `addBook()` cover path unchanged:** The `coverBmpPath` field in `RecentBook` is used for home screen thumbnails, not sleep covers. Since TXT has no thumbnail support, passing `""` remains correct.
+- **HomeActivity::loadRecentCovers() kept as fallback:** Books opened before this change will still have thumbnails generated lazily on the Home screen. No code removal needed.
+
+## Follow-up Items
+
+- Mark todo item as complete in `mod/docs/todo.md`
+- Test on device with each book format (EPUB, XTC/XTCH, TXT)
+- If a new theme is added with a different `homeCoverHeight`, update `PRERENDER_THUMB_HEIGHTS`