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

src/activities/reader/EndOfBookMenuActivity.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <I18n.h>
+
+#include <string>
+#include <vector>
+
+#include "../Activity.h"
+#include "util/ButtonNavigator.h"
+
+class EndOfBookMenuActivity final : public Activity {
+ public:
+  enum class Action {
+    ARCHIVE,
+    DELETE,
+    TABLE_OF_CONTENTS,
+    BACK_TO_BEGINNING,
+    CLOSE_BOOK,
+    CLOSE_MENU,
+  };
+
+  explicit EndOfBookMenuActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, const std::string& bookPath)
+      : Activity("EndOfBookMenu", renderer, mappedInput), bookPath(bookPath) {
+    buildMenuItems();
+  }
+
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+  void render(RenderLock&&) override;
+
+ private:
+  struct MenuItem {
+    Action action;
+    StrId labelId;
+  };
+
+  std::string bookPath;
+  std::vector<MenuItem> menuItems;
+  int selectedIndex = 0;
+  ButtonNavigator buttonNavigator;
+
+  void buildMenuItems();
+};