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/2026-02-13_per-book-letterbox-fill.md

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+# Per-book Letterbox Fill Override
+
+**Date:** 2026-02-13
+**Branch:** mod/fix-edge-fills
+
+## Task
+
+Add the ability to override the sleep cover "letterbox fill mode" on a per-book basis (EPUB only for the menu UI; all book types respected at sleep time).
+
+## Changes Made
+
+### New files
+- `src/util/BookSettings.h` / `src/util/BookSettings.cpp` — Lightweight per-book settings utility. Stores a `letterboxFillOverride` field (0xFF = use global default) in `{cachePath}/book_settings.bin`. Versioned binary format with field count for forward compatibility, matching the pattern used by BookmarkStore and CrossPointSettings.
+
+### Modified files
+- `src/activities/reader/EpubReaderMenuActivity.h` — Added `LETTERBOX_FILL` to the `MenuAction` enum. Added `bookCachePath`, `pendingLetterboxFill`, letterbox fill labels, and helper methods (`letterboxFillToIndex`, `indexToLetterboxFill`, `saveLetterboxFill`). Constructor now accepts a `bookCachePath` parameter and loads the current per-book settings.
+- `src/activities/reader/EpubReaderMenuActivity.cpp` — Handle `LETTERBOX_FILL` action: cycles through Default/Dithered/Solid/None on Confirm (handled locally like `ROTATE_SCREEN`), saves immediately. Renders the current value on the right side of the menu item.
+- `src/activities/reader/EpubReaderActivity.cpp` — Passes `epub->getCachePath()` to the menu activity constructor. Added `ROTATE_SCREEN` and `LETTERBOX_FILL` to the `onReaderMenuConfirm` switch as no-ops to prevent compiler warnings.
+- `src/activities/boot_sleep/SleepActivity.h` — Added `fillModeOverride` parameter to `renderBitmapSleepScreen()`.
+- `src/activities/boot_sleep/SleepActivity.cpp` — `renderCoverSleepScreen()` now loads `BookSettings` from the book's cache path after determining the book type. Passes the per-book override to `renderBitmapSleepScreen()`. `renderBitmapSleepScreen()` uses the override if valid, otherwise falls back to the global `SETTINGS.sleepScreenLetterboxFill`.
+
+## How It Works
+
+1. User opens the EPUB reader menu (Confirm button while reading).
+2. "Letterbox Fill" appears between "Reading Orientation" and "Table of Contents".
+3. Pressing Confirm cycles: Default → Dithered → Solid → None → Default...
+4. The selection is persisted immediately to `book_settings.bin` in the book's cache directory.
+5. When the device enters sleep with the cover screen, the per-book override is loaded and used instead of the global setting (if set).
+6. XTC and TXT books also have their per-book override checked at sleep time, but can only be configured for EPUB via the reader menu (XTC/TXT lack general menus).
+
+## Follow-up Items
+
+- Consider adding the letterbox fill override to XTC/TXT reader menus if those get general menus in the future.
+- The `BookSettings` struct is extensible — other per-book overrides can be added by appending fields and incrementing `BOOK_SETTINGS_COUNT`.