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>

lib/I18n/I18nKeys.h

@@ -119,6 +119,7 @@ enum class StrId : uint16_t {
   STR_CAT_READER,
   STR_CAT_CONTROLS,
   STR_CAT_SYSTEM,
+  STR_CAT_CLOCK,
   STR_SLEEP_SCREEN,
   STR_SLEEP_COVER_MODE,
   STR_STATUS_BAR,
@@ -371,10 +372,24 @@ enum class StrId : uint16_t {
   STR_PREFERRED_PORTRAIT,
   STR_PREFERRED_LANDSCAPE,
   STR_CHOOSE_SOMETHING,
-  STR_HOME_SCREEN_CLOCK,
+  STR_CLOCK,
   STR_CLOCK_AMPM,
   STR_CLOCK_24H,
   STR_SET_TIME,
+  STR_CLOCK_SIZE,
+  STR_CLOCK_SIZE_SMALL,
+  STR_CLOCK_SIZE_MEDIUM,
+  STR_CLOCK_SIZE_LARGE,
+  STR_TIMEZONE,
+  STR_TZ_UTC,
+  STR_TZ_EASTERN,
+  STR_TZ_CENTRAL,
+  STR_TZ_MOUNTAIN,
+  STR_TZ_PACIFIC,
+  STR_TZ_ALASKA,
+  STR_TZ_HAWAII,
+  STR_TZ_CUSTOM,
+  STR_SET_UTC_OFFSET,
   // Sentinel - must be last
   _COUNT
 };