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/util/NumericStepperActivity.cpp

@@ -0,0 +1,104 @@
+#include "NumericStepperActivity.h"
+
+#include <GfxRenderer.h>
+#include <I18n.h>
+
+#include <algorithm>
+#include <cstdio>
+
+#include "ActivityResult.h"
+#include "MappedInputManager.h"
+#include "components/UITheme.h"
+#include "fontIds.h"
+
+void NumericStepperActivity::onEnter() {
+  Activity::onEnter();
+  requestUpdate();
+}
+
+void NumericStepperActivity::onExit() { Activity::onExit(); }
+
+void NumericStepperActivity::loop() {
+  if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+    ActivityResult r;
+    r.isCancelled = true;
+    setResult(std::move(r));
+    finish();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+    setResult(PageResult{.page = static_cast<uint32_t>(value)});
+    finish();
+    return;
+  }
+
+  // Side buttons: ±1
+  if (mappedInput.wasPressed(MappedInputManager::Button::Up)) {
+    if (value < maxValue) {
+      value++;
+      requestUpdate();
+    }
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Down)) {
+    if (value > minValue) {
+      value--;
+      requestUpdate();
+    }
+    return;
+  }
+
+  // Front face buttons: ±10
+  if (mappedInput.wasPressed(MappedInputManager::Button::Right)) {
+    value = std::min(value + 10, maxValue);
+    requestUpdate();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Left)) {
+    value = std::max(value - 10, minValue);
+    requestUpdate();
+    return;
+  }
+}
+
+void NumericStepperActivity::render(RenderLock&&) {
+  renderer.clearScreen();
+
+  const auto pageWidth = renderer.getScreenWidth();
+  const int lineHeight12 = renderer.getLineHeight(UI_12_FONT_ID);
+
+  const auto& metrics = UITheme::getInstance().getMetrics();
+  GUI.drawHeader(renderer, Rect{0, metrics.topPadding, pageWidth, metrics.headerHeight}, title.c_str());
+
+  char valueStr[16];
+  snprintf(valueStr, sizeof(valueStr), "%d", value);
+
+  const int textWidth = renderer.getTextWidth(UI_12_FONT_ID, valueStr);
+  const int startX = (pageWidth - textWidth) / 2;
+  const int valueY = metrics.topPadding + metrics.headerHeight + 60;
+
+  constexpr int highlightPad = 10;
+  renderer.fillRoundedRect(startX - highlightPad, valueY - 4, textWidth + highlightPad * 2, lineHeight12 + 8, 6,
+                           Color::LightGray);
+  renderer.drawText(UI_12_FONT_ID, startX, valueY, valueStr, true);
+
+  const int arrowX = pageWidth / 2;
+  const int arrowUpY = valueY - 20;
+  const int arrowDownY = valueY + lineHeight12 + 12;
+  constexpr int arrowSize = 6;
+  for (int row = 0; row < arrowSize; row++) {
+    renderer.drawLine(arrowX - row, arrowUpY + row, arrowX + row, arrowUpY + row);
+  }
+  for (int row = 0; row < arrowSize; row++) {
+    renderer.drawLine(arrowX - row, arrowDownY + arrowSize - 1 - row, arrowX + row, arrowDownY + arrowSize - 1 - row);
+  }
+
+  const auto labels = mappedInput.mapLabels(tr(STR_BACK), tr(STR_SAVE), "-10", "+10");
+  GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+  GUI.drawSideButtonHints(renderer, "+1", "-1");
+
+  renderer.displayBuffer();
+}