mod: add clock settings tab, timezone support, and clock size option

Fix clock persistence bug caused by stale legacy read in settings
deserialization. Add clock size setting (Small/Medium/Large) and
timezone selection with North American presets plus custom UTC offset.
Move all clock-related settings into a dedicated Clock tab, rename
"Home Screen Clock" to "Clock", and move minute-change detection to
main loop so the header clock updates on every screen.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/activities/settings/SetTimezoneOffsetActivity.cpp

@@ -0,0 +1,101 @@
+#include "SetTimezoneOffsetActivity.h"
+
+#include <GfxRenderer.h>
+#include <I18n.h>
+
+#include <cstdio>
+#include <cstdlib>
+
+#include "CrossPointSettings.h"
+#include "MappedInputManager.h"
+#include "components/UITheme.h"
+#include "fontIds.h"
+
+void SetTimezoneOffsetActivity::onEnter() {
+  Activity::onEnter();
+  offsetHours = SETTINGS.timezoneOffsetHours;
+  requestUpdate();
+}
+
+void SetTimezoneOffsetActivity::onExit() { Activity::onExit(); }
+
+void SetTimezoneOffsetActivity::loop() {
+  if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+    onBack();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+    SETTINGS.timezoneOffsetHours = offsetHours;
+    SETTINGS.saveToFile();
+    // Apply timezone immediately
+    setenv("TZ", SETTINGS.getTimezonePosixStr(), 1);
+    tzset();
+    onBack();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Up)) {
+    if (offsetHours < 14) {
+      offsetHours++;
+      requestUpdate();
+    }
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Down)) {
+    if (offsetHours > -12) {
+      offsetHours--;
+      requestUpdate();
+    }
+    return;
+  }
+}
+
+void SetTimezoneOffsetActivity::render(Activity::RenderLock&&) {
+  renderer.clearScreen();
+
+  const auto pageWidth = renderer.getScreenWidth();
+  const int lineHeight12 = renderer.getLineHeight(UI_12_FONT_ID);
+
+  // Title
+  renderer.drawCenteredText(UI_12_FONT_ID, 20, tr(STR_SET_UTC_OFFSET), true, EpdFontFamily::BOLD);
+
+  // Format the offset string
+  char offsetStr[16];
+  if (offsetHours >= 0) {
+    snprintf(offsetStr, sizeof(offsetStr), "UTC+%d", offsetHours);
+  } else {
+    snprintf(offsetStr, sizeof(offsetStr), "UTC%d", offsetHours);
+  }
+
+  const int textWidth = renderer.getTextWidth(UI_12_FONT_ID, offsetStr);
+  const int startX = (pageWidth - textWidth) / 2;
+  const int valueY = 80;
+
+  // Draw selection highlight
+  constexpr int highlightPad = 10;
+  renderer.fillRoundedRect(startX - highlightPad, valueY - 4, textWidth + highlightPad * 2, lineHeight12 + 8, 6,
+                           Color::LightGray);
+
+  // Draw the offset text
+  renderer.drawText(UI_12_FONT_ID, startX, valueY, offsetStr, true);
+
+  // Draw up/down arrows
+  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);
+  }
+
+  // Button hints
+  const auto labels = mappedInput.mapLabels(tr(STR_BACK), tr(STR_SAVE), tr(STR_DIR_UP), tr(STR_DIR_DOWN));
+  GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+
+  renderer.displayBuffer();
+}