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

lib/Epub/Epub/TableData.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <memory>
+#include <vector>
+
+#include "ParsedText.h"
+#include "css/CssStyle.h"
+
+/// A single cell in a table row.
+struct TableCell {
+  std::unique_ptr<ParsedText> content;
+  bool isHeader = false;  // true for <th>, false for <td>
+  int colspan = 1;        // number of logical columns this cell spans
+  CssLength widthHint;    // width hint from HTML attribute or CSS (if hasWidthHint)
+  bool hasWidthHint = false;
+};
+
+/// A single row in a table.
+struct TableRow {
+  std::vector<TableCell> cells;
+};
+
+/// Buffered table data collected during SAX parsing.
+/// The entire table must be buffered before layout because column widths
+/// depend on content across all rows.
+struct TableData {
+  std::vector<TableRow> rows;
+  std::vector<CssLength> colWidthHints;  // width hints from <col> tags, indexed by logical column
+};