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/SettingsActivity.cpp

@@ -3,6 +3,9 @@
 #include <GfxRenderer.h>
 #include <Logging.h>
 
+#include <algorithm>
+#include <cstdlib>
+
 #include "ButtonRemapActivity.h"
 #include "CalibreSettingsActivity.h"
 #include "ClearCacheActivity.h"
@@ -12,19 +15,22 @@
 #include "MappedInputManager.h"
 #include "OtaUpdateActivity.h"
 #include "SetTimeActivity.h"
+#include "SetTimezoneOffsetActivity.h"
 #include "SettingsList.h"
 #include "activities/network/WifiSelectionActivity.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
 
 const StrId SettingsActivity::categoryNames[categoryCount] = {StrId::STR_CAT_DISPLAY, StrId::STR_CAT_READER,
-                                                              StrId::STR_CAT_CONTROLS, StrId::STR_CAT_SYSTEM};
+                                                              StrId::STR_CAT_CONTROLS, StrId::STR_CAT_SYSTEM,
+                                                              StrId::STR_CAT_CLOCK};
 
 void SettingsActivity::onEnter() {
   Activity::onEnter();
 
   // Build per-category vectors from the shared settings list
   displaySettings.clear();
+  clockSettings.clear();
   readerSettings.clear();
   controlsSettings.clear();
   systemSettings.clear();
@@ -33,6 +39,8 @@ void SettingsActivity::onEnter() {
     if (setting.category == StrId::STR_NONE_OPT) continue;
     if (setting.category == StrId::STR_CAT_DISPLAY) {
       displaySettings.push_back(std::move(setting));
+    } else if (setting.category == StrId::STR_CAT_CLOCK) {
+      clockSettings.push_back(std::move(setting));
     } else if (setting.category == StrId::STR_CAT_READER) {
       readerSettings.push_back(std::move(setting));
     } else if (setting.category == StrId::STR_CAT_CONTROLS) {
@@ -44,7 +52,7 @@ void SettingsActivity::onEnter() {
   }
 
   // Append device-only ACTION items
-  displaySettings.push_back(SettingInfo::Action(StrId::STR_SET_TIME, SettingAction::SetTime));
+  rebuildClockActions();
   controlsSettings.insert(controlsSettings.begin(),
                           SettingInfo::Action(StrId::STR_REMAP_FRONT_BUTTONS, SettingAction::RemapFrontButtons));
   systemSettings.push_back(SettingInfo::Action(StrId::STR_WIFI_NETWORKS, SettingAction::Network));
@@ -136,6 +144,9 @@ void SettingsActivity::loop() {
       case 3:
         currentSettings = &systemSettings;
         break;
+      case 4:
+        currentSettings = &clockSettings;
+        break;
     }
     settingsCount = static_cast<int>(currentSettings->size());
   }
@@ -207,6 +218,9 @@ void SettingsActivity::toggleCurrentSetting() {
       case SettingAction::SetTime:
         enterSubActivity(new SetTimeActivity(renderer, mappedInput, onComplete));
         break;
+      case SettingAction::SetTimezoneOffset:
+        enterSubActivity(new SetTimezoneOffsetActivity(renderer, mappedInput, onComplete));
+        break;
       case SettingAction::None:
         // Do nothing
         break;
@@ -216,6 +230,37 @@ void SettingsActivity::toggleCurrentSetting() {
   }
 
   SETTINGS.saveToFile();
+
+  // Apply timezone whenever settings change (idempotent, cheap)
+  setenv("TZ", SETTINGS.getTimezonePosixStr(), 1);
+  tzset();
+
+  // Rebuild clock actions (show/hide "Set UTC Offset" based on timezone selection)
+  rebuildClockActions();
+}
+
+void SettingsActivity::rebuildClockActions() {
+  // Remove any existing ACTION items from clockSettings (keep enum settings from getSettingsList)
+  clockSettings.erase(std::remove_if(clockSettings.begin(), clockSettings.end(),
+                                     [](const SettingInfo& s) { return s.type == SettingType::ACTION; }),
+                      clockSettings.end());
+
+  // Always add Set Time
+  clockSettings.push_back(SettingInfo::Action(StrId::STR_SET_TIME, SettingAction::SetTime));
+
+  // Only add Set UTC Offset when timezone is set to Custom
+  if (SETTINGS.timezone == CrossPointSettings::TZ_CUSTOM) {
+    clockSettings.push_back(SettingInfo::Action(StrId::STR_SET_UTC_OFFSET, SettingAction::SetTimezoneOffset));
+  }
+
+  // Update settingsCount if we're currently viewing the clock category
+  if (currentSettings == &clockSettings) {
+    settingsCount = static_cast<int>(clockSettings.size());
+    // Clamp selection to avoid pointing past the end of the list
+    if (selectedSettingIndex > settingsCount) {
+      selectedSettingIndex = settingsCount;
+    }
+  }
 }
 
 void SettingsActivity::render(Activity::RenderLock&&) {