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/util/TimeSync.cpp

@@ -5,6 +5,10 @@
 #include <freertos/FreeRTOS.h>
 #include <freertos/task.h>
 
+#include <cstdlib>
+
+#include "CrossPointSettings.h"
+
 namespace TimeSync {
 
 void startNtpSync() {
@@ -12,6 +16,10 @@ void startNtpSync() {
     esp_sntp_stop();
   }
 
+  // Apply timezone so NTP-synced time is displayed correctly
+  setenv("TZ", SETTINGS.getTimezonePosixStr(), 1);
+  tzset();
+
   esp_sntp_setoperatingmode(ESP_SNTP_OPMODE_POLL);
   esp_sntp_setservername(0, "pool.ntp.org");
   esp_sntp_init();