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_mod-version-env.md

@@ -0,0 +1,23 @@
+# Add `env:mod` with version + git hash
+
+## Task
+Add a PlatformIO environment that flashes firmware with a `-mod+<git_hash>` version suffix (e.g. `1.0.0-mod+a3f7c21`).
+
+## Changes
+
+### New file: `scripts/inject_mod_version.py`
+- PlatformIO pre-build script
+- Reads `version` from the `[crosspoint]` section of `platformio.ini`
+- Runs `git rev-parse --short HEAD` to get the current commit hash
+- Injects `-DCROSSPOINT_VERSION="{version}-mod+{hash}"` into build flags
+
+### Modified: `platformio.ini`
+- Added `[env:mod]` section (lines 58-64) that extends `base`, includes the new script via `extra_scripts`, and inherits base build flags
+
+## Usage
+```
+pio run -e mod -t upload
+```
+
+## Follow-up
+- None