refactor(eink): Text size and Icon size as schema settings, on opt-in builds only

Review follow-up:

- The rows exist only where the build asks for them: Text size with
  EINK_FONT_SCALE, Icon size with STATUS_ICON_SCALE. The stock 2.13", the
  portrait builds and the L2 don't get them -- their screens are laid out
  for one cell size. The text override also applies in landscape only.
- Stored in NodePrefs (ui_text_scale, ui_icon_scale) instead of a
  /ui_scale file, as rows in the schema's Display section: the usual row,
  save path and factory reset, and console keys display.text.size /
  display.icon.size. The hand-written Settings rows and the load/save code
  are gone; UITask::applyUiScale() applies the prefs at boot and on change
  (applyDisplayPrefs). On opt-in builds ui_text_scale starts at the
  build's EINK_FONT_SCALE (DataStore sanitize), so the row shows the scale
  in use.
- EINK_FONT_SCALE, when set, now scales whichever landscape font the build
  picks (the 6x9, or the EINK_LARGE_FONT one); unset, it is stock as before.
- setUiScale() skips the re-layout and full redraw when nothing changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/DataStore.cpp

@@ -334,6 +334,11 @@ static void sanitize(NodePrefs& p) {
   flag(p.lock_compact, 0);
   flag(p.ble_off, 0);
   if (p.msg_alert > NodePrefs::MSG_ALERT_OFF) p.msg_alert = NodePrefs::MSG_ALERT_NORMAL;
+  if (p.ui_text_scale > NodePrefs::UI_TEXT_SCALE_MAX) p.ui_text_scale = 0;
+#ifdef EINK_FONT_SCALE   // the Text size row shows the scale in use: start at the build's
+  if (p.ui_text_scale == 0) p.ui_text_scale = EINK_FONT_SCALE;
+#endif
+  if (p.ui_icon_scale > NodePrefs::UI_ICON_SCALE_MAX) p.ui_icon_scale = 0;
   if (!p.ch_scope_follow) {
     for (uint8_t i = 0; i < NodePrefs::MAX_SCOPED_CHANNELS; i++)
       if (p.ch_scope_idx[i] == 0) p.ch_scope_idx[i] = NodePrefs::CH_SCOPE_DEFAULT;