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/home/HomeActivity.cpp

@@ -11,7 +11,6 @@
 
 #include <cstdio>
 #include <cstring>
-#include <ctime>
 #include <vector>
 
 #include "Battery.h"
@@ -192,19 +191,6 @@ void HomeActivity::freeCoverBuffer() {
 }
 
 void HomeActivity::loop() {
-  // Refresh the screen when the displayed minute changes (clock update)
-  if (SETTINGS.homeScreenClock != CrossPointSettings::CLOCK_OFF) {
-    time_t now = time(nullptr);
-    struct tm* t = localtime(&now);
-    if (t != nullptr && t->tm_year > 100) {
-      const int currentMinute = t->tm_hour * 60 + t->tm_min;
-      if (lastRenderedMinute >= 0 && currentMinute != lastRenderedMinute) {
-        requestUpdate();
-      }
-      lastRenderedMinute = currentMinute;
-    }
-  }
-
   const int menuCount = getMenuItemCount();
 
   buttonNavigator.onNext([this, menuCount] {