feat: runtime font switcher — Default vs Lemon in Settings > Display

- Add Lemon font (LemonFont.h, LemonIcons.h) to the standard build
  alongside the Adafruit built-in font; ~101 KB added to flash
- SH1106Display: add _use_lemon flag + setLemonFont(bool) to switch
  at runtime; print() and getTextWidth() use Lemon path when active;
  translateUTF8ToBlocks() passes UTF-8 through unchanged (Lemon supports
  full Unicode U+0020-U+04FF) vs transliterating for the default font
- DisplayDriver: add getCharWidth()/getLineHeight() virtuals (defaults 6/8);
  SH1106Display returns 5/9 for Lemon, 6/8 for default; add setLemonFont()
  no-op virtual; fix orphaned UTF-8 leading byte in drawTextEllipsized
- FullscreenMsgView: replace fixed-char-count word-wrap with pixel-accurate
  wrap using display.getTextWidth(); use getLineHeight() for spacing so
  Lemon (9 px) and default (8 px) both render correctly
- NodePrefs: add use_lemon_font field (0=default, 1=Lemon)
- SettingsScreen: add "Font" item in Display section (Default / Lemon),
  calls UITask::applyFont() on change
- UITask: add applyFont() that calls display->setLemonFont(use_lemon_font);
  called at startup (begin()) and when the setting changes

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

examples/companion_radio/ui-new/UITask.cpp

@@ -816,6 +816,7 @@ void UITask::begin(DisplayDriver* display, SensorManager* sensors, NodePrefs* no
   setCurrScreen(splash);
 
   applyBrightness();
+  applyFont();
 }
 
 void UITask::gotoSettingsScreen() {
@@ -1557,6 +1558,12 @@ void UITask::applyBrightness() {
   }
 }
 
+void UITask::applyFont() {
+  if (_display != NULL && _node_prefs != NULL) {
+    _display->setLemonFont(_node_prefs->use_lemon_font != 0);
+  }
+}
+
 void UITask::setBrightnessLevel(uint8_t level) {
   if (_node_prefs == NULL) return;
   if (level > 4) level = 4;