refactor(ui): audit-pass fixes + dead-code/redundancy cleanup

Fixes from a full ui-new audit (OLED + e-ink both build green):
- remove dead DisplayDriver::drawScrollArrows (all lists use drawScrollIndicator)
- SettingsScreen selection bar -> lineStep()-1, matching the drawList screens
- HomeScreen: don't force the 1s blink refresh on the CLOCK page (status icons
  are hidden there anyway)
- FullscreenMsgView: clamp KEY_DOWN scroll to a cached _max_scroll instead of
  over-incrementing and leaning on the next render to clamp
- DataStore: clamp use_lemon_font (>1 -> 0) on load, like the other enum fields
- move the ~1.5KB wrap scratch (trans/lines) off the render stack into shared
  file-scope statics in FullscreenMsgView (single-threaded UI; the fullscreen
  view and history list never lay out in the same frame)

Cleanup:
- drop dead members RingtoneEditorScreen::DUR_VALS and HomeScreen::sensors_scroll
- delete redundant manual scroll-clamps in handleInput across the drawList
  screens (drawList already reclamps each render); remove the now-unused _visible
  from QuickMsgScreen/NearbyScreen/BotScreen and BotScreen::scrollToSel()

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/DataStore.cpp

@@ -338,6 +338,9 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
   // can leave stray bytes here, so clamp out-of-range values back to defaults.
   // Values for notif_melody_ad: 0=built-in, 1=melody1, 2=melody2, 3=none.
   if (_prefs.notif_melody_ad > 3) _prefs.notif_melody_ad = 0;
+  // A stale value >1 from an older multi-font build would read as "Lemon" (all
+  // sites test != 0) until the user toggles Font; clamp it to default here.
+  if (_prefs.use_lemon_font  > 1) _prefs.use_lemon_font  = 0;
   if (_prefs.units_imperial  > 1) _prefs.units_imperial  = 0;
   if (_prefs.trail_show_pace > 1) _prefs.trail_show_pace = 0;
   if (_prefs.advert_sound_scope > 1) _prefs.advert_sound_scope = ADVERT_SOUND_SCOPE_ALL;