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/2026-02-09_00-00-summary.md

@@ -0,0 +1,21 @@
+# Project Documentation for CrossPoint Reader Firmware
+
+**Date:** 2026-02-09
+
+## Task
+
+Create three documentation files in `/mod/docs/` covering the Xteink X4 hardware capabilities, project file structure, and CI/build/code style for the CrossPoint Reader firmware.
+
+## Changes Made
+
+### New Files
+
+1. **`mod/docs/hardware.md`** -- Device hardware capabilities documentation covering CPU (ESP32-C3), 16MB flash with partition layout, 480x800 eink display (2-bit grayscale, 3 refresh modes), 7 physical buttons, SD card storage, battery monitoring, WiFi networking, USB-C, and power management (deep sleep with GPIO wakeup).
+
+2. **`mod/docs/file-structure.md`** -- Complete project file structure map documenting `src/` (main app with Activity-based UI system), `lib/` (16 libraries including EPUB engine, HAL, fonts, XML/ZIP/JPEG support), `open-x4-sdk/` (hardware driver submodule), `scripts/` (build helpers), `test/` (hyphenation tests), `docs/` (upstream docs), and `.github/` (CI/templates).
+
+3. **`mod/docs/ci-build-and-code-style.md`** -- CI pipeline documentation covering 4 GitHub Actions workflows (CI with format/cppcheck/build/gate jobs, release, RC, PR title check), PlatformIO build system with 3 environments, clang-format 21 rules (2-space indent, 120-col limit, K&R braces), cppcheck static analysis config, and contribution guidelines (semantic PR titles, AI disclosure, scope alignment).
+
+## Follow-up Items
+
+- None. All three documents are complete and ready for review.