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/CrossPointSettings.h

@@ -131,6 +131,22 @@ class CrossPointSettings {
   // Home screen clock format
   enum CLOCK_FORMAT { CLOCK_OFF = 0, CLOCK_AMPM = 1, CLOCK_24H = 2, CLOCK_FORMAT_COUNT };
 
+  // Clock size
+  enum CLOCK_SIZE { CLOCK_SIZE_SMALL = 0, CLOCK_SIZE_MEDIUM = 1, CLOCK_SIZE_LARGE = 2, CLOCK_SIZE_COUNT };
+
+  // Timezone presets
+  enum TIMEZONE {
+    TZ_UTC = 0,
+    TZ_EASTERN = 1,
+    TZ_CENTRAL = 2,
+    TZ_MOUNTAIN = 3,
+    TZ_PACIFIC = 4,
+    TZ_ALASKA = 5,
+    TZ_HAWAII = 6,
+    TZ_CUSTOM = 7,
+    TZ_COUNT
+  };
+
   // Sleep screen settings
   uint8_t sleepScreen = DARK;
   // Sleep screen cover mode settings
@@ -192,8 +208,15 @@ class CrossPointSettings {
   uint8_t preferredPortrait = PORTRAIT;
   uint8_t preferredLandscape = LANDSCAPE_CW;
 
-  // Home screen clock display format (OFF by default)
-  uint8_t homeScreenClock = CLOCK_OFF;
+  // Clock display format (OFF by default)
+  uint8_t clockFormat = CLOCK_OFF;
+  // Clock display size
+  uint8_t clockSize = CLOCK_SIZE_SMALL;
+
+  // Timezone setting
+  uint8_t timezone = TZ_UTC;
+  // Custom timezone offset in hours from UTC (-12 to +14)
+  int8_t timezoneOffsetHours = 0;
 
   ~CrossPointSettings() = default;
 
@@ -214,6 +237,7 @@ class CrossPointSettings {
   float getReaderLineCompression() const;
   unsigned long getSleepTimeoutMs() const;
   int getRefreshFrequency() const;
+  const char* getTimezonePosixStr() const;
 };
 
 // Helper macro to access settings