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/2026-02-16_05-30-summary.md

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+# Port PR #838 and PR #907 into fork
+
+## Task
+Cherry-pick / manually port two upstream PRs into the fork:
+- **PR #907**: Cover image outlines to improve legibility
+- **PR #838**: Fallback logic for epub cover extraction
+
+## Changes Made
+
+### PR #907 (cover outlines) — `src/components/themes/lyra/LyraTheme.cpp`
+- Always draw a rectangle outline around cover tiles before drawing the bitmap on top
+- Removed `hasCover` flag — simplified logic so outline is always present, preventing low-contrast covers from blending into the background
+
+### PR #838 (cover fallback logic) — 3 files
+
+#### `lib/Epub/Epub.h`
+- Added declarations for 4 new methods: `generateInvalidFormatCoverBmp`, `generateInvalidFormatThumbBmp`, `isValidThumbnailBmp` (static), `getCoverCandidates` (private)
+- Added doc comments on existing `generateCoverBmp` and `generateThumbBmp`
+
+#### `lib/Epub/Epub.cpp`
+- Added `#include <HalDisplay.h>` and `#include <algorithm>`
+- **`generateCoverBmp`**: Added invalid BMP detection/retry, cover fallback candidate probing (`getCoverCandidates`), case-insensitive extension checking. Returns `false` on failure (no internal X-pattern fallback) so callers control the fallback chain
+- **`generateThumbBmp`**: Same changes as `generateCoverBmp` — invalid BMP detection, fallback probing, case-insensitive check. Returns `false` on failure (no internal X-pattern fallback) so callers control the fallback chain
+- **`generateInvalidFormatThumbBmp`** (new): Creates 1-bit BMP with X pattern as thumbnail marker
+- **`generateInvalidFormatCoverBmp`** (new): Creates 1-bit BMP with X pattern as cover marker, using display dimensions
+- **`isValidThumbnailBmp`** (new, static): Validates BMP by checking file size > 0 and 'BM' header
+- **`getCoverCandidates`** (new, private): Returns list of common cover filenames to probe
+
+#### `src/activities/home/HomeActivity.cpp`
+- Replaced `Storage.exists()` check with `Epub::isValidThumbnailBmp()` to catch corrupt/empty thumbnails
+- Added epub.load retry logic (cache-only first, then full build)
+- After successful thumbnail generation, update `RECENT_BOOKS` with the new thumb path
+- Thumbnail fallback chain: Real Cover → PlaceholderCoverGenerator → X-Pattern marker (epub only; xtc/other formats fall back to placeholder only)
+
+## Adaptations from upstream PR
+- All `Serial.printf` calls converted to `LOG_DBG`/`LOG_ERR` macros (fork convention)
+- No `#include <HardwareSerial.h>` (not needed with Logging.h)
+- Retained fork's `bookMetadataCache` null-check guards
+- HomeActivity changes manually adapted to fork's `loadRecentCovers()` structure (upstream has inline code in a different method)
+- Fork's `PlaceholderCoverGenerator` is the preferred fallback; X-pattern marker is last resort only
+
+#### `src/activities/boot_sleep/SleepActivity.cpp`
+- EPUB sleep screen cover now follows Real Cover → Placeholder → X-Pattern fallback chain
+- Upgraded `Storage.exists()` check to `Epub::isValidThumbnailBmp()` for the epub cover path
+
+#### `src/activities/reader/EpubReaderActivity.cpp`
+- Cover and thumbnail pre-rendering now follows Real Cover → Placeholder → X-Pattern fallback chain
+- Upgraded all `Storage.exists()` checks to `Epub::isValidThumbnailBmp()` for cover/thumb paths
+
+## Follow-up Items
+- Build and test on device to verify cover generation pipeline works end-to-end