WioTrackerL1 UI: predefined messages, caps lock, placeholder picker, 139-char limit

- Settings → Messages section: 10 user-editable message slots (M1–M10)
  with on-screen keyboard editor; slot M1 defaults to "OK" on first boot
- Keyboard: add Caps Lock [^] button — stays highlighted when active,
  all letters display and insert as uppercase until toggled off
- Keyboard: add [{}] placeholder picker overlay — inserts {loc} or {time}
  into the message at cursor position; available in both compose and
  settings slot editor
- Max message length raised to 139 chars to match the companion app;
  ChHistEntry text buffer extended to 140 chars
- NodePrefs: custom_msgs slot size extended to 140 chars per slot
- KB constants (KB_MAX_LEN, KB_CHARS, etc.) moved before SettingsScreen
  so both SettingsScreen and QuickMsgScreen can reference them

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/NodePrefs.h

@@ -39,4 +39,5 @@ struct NodePrefs {  // persisted to file
   int8_t tz_offset_hours;       // timezone offset from UTC, -12..+14 (default 0)
   uint16_t low_batt_mv;         // auto-shutdown threshold: 0=disabled, 3000-3500 mV
   uint8_t batt_display_mode;   // 0=icon, 1=percent, 2=voltage
+  char custom_msgs[10][140];   // user-defined quick messages (supports {loc}, {time})
 };