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>

src/helpers/ui/EinkGfxDisplay.h

@@ -29,7 +29,7 @@ class EinkGfxDisplay : public DisplayDriver {
   uint16_t _curr;
   const GFXfont* _font;
   int _cell_w = 6, _cell_h = 9;  // the font's cell, before _px and the text size
-  int _px = 1;                   // pixel doubling (landscape without EINK_LARGE_FONT)
+  int _px = 1;                   // pixel multiplier (landscape: EINK_FONT_PX, or Text size)
   uint8_t _px_override = 0;      // Settings > Display > Text size (0 = build default)
   int _text_sz = 1;
   int _cx = 0, _cy = 0;          // cursor, top of the text row
@@ -77,7 +77,11 @@ public:
   bool isEink() override { return true; }
   // Runtime text scale (Settings > Display > Text size): re-lays out and forces
   // a full redraw. 0 = the build default (EINK_FONT_SCALE).
-  void setUiScale(uint8_t font_scale) override { _px_override = font_scale; updateLayout(); }
+  void setUiScale(uint8_t font_scale) override {
+    if (font_scale == _px_override) return;   // unchanged: no full redraw
+    _px_override = font_scale;
+    updateLayout();
+  }
 
   void startFrame(Color bkg = DARK) override;
   void setTextSize(int sz) override;

src/helpers/ui/EinkGfxDisplayImpl.h

@@ -3,11 +3,15 @@
 // the font tables below are static arrays.
 
 #include "EinkGfxDisplay.h"
-// EINK_FONT_SCALE=<n>: pixel multiplier for the 6x9 font on a landscape panel
-// without EINK_LARGE_FONT (default 2). 4 on an 800x480 panel = 24x36 cells,
-// ~33 characters x 13 lines. Settings > Display > Text size overrides it at run time.
-#ifndef EINK_FONT_SCALE
-  #define EINK_FONT_SCALE 2
+// EINK_FONT_SCALE=<n>: pixel multiplier for the landscape font -- the 6x9, or
+// the EINK_LARGE_FONT one if the build picks it. 4 on an 800x480 panel with the
+// 6x9 = 24x36 cells, ~33 characters x 13 lines. Setting it also adds Settings >
+// Display > Text size, which overrides it at run time. Unset: stock, the 6x9 at
+// 2x or the large font at its own size.
+#ifdef EINK_FONT_SCALE
+  #define EINK_FONT_PX EINK_FONT_SCALE
+#else
+  #define EINK_FONT_PX (EINK_LARGE_FONT ? 1 : 2)
 #endif
 #include "MiscFixedRenderer.h"
 #if EINK_LARGE_FONT == 2
@@ -26,8 +30,8 @@ EinkGfxDisplay::EinkGfxDisplay(int w, int h, Adafruit_GFX& gfx, uint16_t ink, ui
 void EinkGfxDisplay::updateLayout() {
   const bool landscape = width() >= height();
   _font = (EINK_LARGE_FONT && landscape) ? &EINK_LARGE_GFXFONT : &MiscFixed;
-  _px = (!EINK_LARGE_FONT && landscape) ? EINK_FONT_SCALE : 1;
-  if (_px_override) _px = _px_override;
+  _px = landscape ? EINK_FONT_PX : 1;
+  if (_px_override && landscape) _px = _px_override;   // portrait screens are laid out for 1x
   _cell_w = miscFixedCellW(*_font);
   _cell_h = _font->yAdvance;
   _vw_dirty = true;