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_upstream-sync-summary.md

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+# Upstream Sync: `upstream/master` into `mod/master`
+
+**Date:** 2026-02-16  
+**Task:** Synchronize recent upstream changes into the mod fork while preserving all mod-specific features.
+
+## Strategy
+
+- **Cherry-pick** approach (not full merge) for granular control
+- 13 upstream commits cherry-picked across 3 phases; 4 skipped (mod already had enhanced implementations)
+- Working branch `mod/sync-upstream` used, then fast-forwarded into `mod/master`
+
+## Phases & Commits
+
+### Phase 1 — Low-risk (6 commits)
+| PR | Description | Notes |
+|----|-------------|-------|
+| #689 | Hyphenation optimization | Naming conflict resolved (mod's `OMIT_HYPH_*` guards preserved) |
+| #832 | Settings size auto-calc | Mod's `sleepScreenLetterboxFill` added to new `SettingsWriter` |
+| #840 | clang-format-fix shebang | Clean |
+| #917 | SCOPE.md dictionary docs | Clean |
+| #856 | Multiple author display | Clean |
+| #858 | Miniz compilation warning | Clean |
+
+### Phase 2 — Major refactors (3 commits)
+| PR | Description | Notes |
+|----|-------------|-------|
+| #774 | Activity render() refactor | ~15 conflicts. Mod's 5 custom activities (Bookmarks, Dictionary) adapted to new `render(RenderLock&&)` pattern. Deadlock in `EpubReaderActivity.cpp` identified and fixed (redundant mutex around `enterNewActivity()`). |
+| #916 | RAII RenderLock | Clean cherry-pick + audit of mod code for manual mutex usage |
+| #728 | I18n system | ~15-20 conflicts. 16 new `StrId` keys added for mod strings. `DynamicEnum` font handling preserved. `SettingsList.h` and `SettingsActivity.cpp` adapted. |
+
+### Phase 3 — Post-I18n fixes (4 commits)
+| PR | Description | Notes |
+|----|-------------|-------|
+| #884 | Empty button icon fix | Clean |
+| #906 | Webserver docs update | Clean |
+| #792 | Translators doc | Clean |
+| #796 | Battery icon alignment | Clean |
+
+### Mod adaptation commits (3)
+- `mod: adapt mod activities to #774 render() pattern` — Systematic refactor of 5 activity pairs
+- `mod: convert remaining manual render locks to RAII RenderLock` — Audit & cleanup
+- `mod: remove duplicate I18n.h include in HomeActivity.cpp` — Cleanup
+
+## Skipped Upstream Commits (4)
+- #676, #700 (image/cover improvements) — Mod already has enhanced pipeline
+- #668 (JPEG support) — Already in mod
+- #780 (cover fallback) — Already cherry-picked into mod
+
+## Files Changed
+111 files changed, ~23,700 insertions, ~17,700 deletions across hyphenation tries, I18n system, activity refactors, and documentation.
+
+## Key Decisions
+- **Image pipeline:** Kept mod's versions entirely; upstream's cover fixes were already ported
+- **Deadlock fix:** Removed redundant `xSemaphoreTake`/`xSemaphoreGive` around `enterNewActivity()` in `EpubReaderActivity.cpp` — the new `RenderLock` inside `enterNewActivity()` would deadlock with the outer manual lock
+- **I18n integration:** Added mod-specific `StrId` keys rather than keeping hardcoded strings
+
+## Verification
+- All mod features (bookmarks, dictionary, letterbox fill, placeholder covers, table rendering, embedded images) verified for code-path integrity post-sync
+- No broken references or missing dependencies found
+
+## Follow-up Items
+- Full PlatformIO build on hardware to confirm compilation
+- Runtime testing of all mod features on device