feat: add Char Test screen and extend Lemon font to Greek/Cyrillic

- Add CharTestScreen showing sample characters from 11 scripts
  (PL, DE, CS, FR, NO, HU, HR, TR, LT, Cyrillic, Greek) as raw
  UTF-8 to verify native font rendering without transliteration
- Add "Char Test" entry to ToolsScreen menu
- Regenerate LemonFont.h from lemon.bdf with full U+0020–U+04FF
  range: 1074 BDF glyphs + 174 placeholders, 4111 bitmap bytes;
  adds Greek (137 glyphs) and Cyrillic (256 glyphs) coverage;
  also fixes space advance (DWIDTH=5, was BBX+1=1)

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

examples/companion_radio/ui-new/UITask.cpp

@@ -127,6 +127,7 @@ static const uint16_t HP_ALL       = 0x01FF;
 #include "NearbyScreen.h"
 #include "DashboardConfigScreen.h"
 #include "AutoAdvertScreen.h"
+#include "CharTestScreen.h"
 #include "ToolsScreen.h"
 
 // ── HomeScreen ────────────────────────────────────────────────────────────────
@@ -808,6 +809,7 @@ void UITask::begin(DisplayDriver* display, SensorManager* sensors, NodePrefs* no
   nearby_screen = new NearbyScreen(this);
   dashboard_config = new DashboardConfigScreen(this, node_prefs);
   auto_advert_screen = new AutoAdvertScreen(this, node_prefs);
+  char_test_screen   = new CharTestScreen(this);
   setCurrScreen(splash);
 
   applyBrightness();
@@ -847,6 +849,11 @@ void UITask::gotoAutoAdvertScreen() {
   setCurrScreen(auto_advert_screen);
 }
 
+void UITask::gotoCharTestScreen() {
+  ((CharTestScreen*)char_test_screen)->enter();
+  setCurrScreen(char_test_screen);
+}
+
 void UITask::playMelody(const char* melody) {
 #ifdef PIN_BUZZER
   buzzer.playForced(melody);