feat: add runtime display rotation setting for e-ink builds

Adds Settings > Display > Rotation (0°/90°/180°/270°) that persists to
NodePrefs and is applied on startup. Falls back to compile-time
DISPLAY_ROTATION when the field is missing from an older prefs file.

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

src/helpers/ui/DisplayDriver.h

@@ -7,6 +7,7 @@ class DisplayDriver {
   int _w, _h;
 protected:
   DisplayDriver(int w, int h) { _w = w; _h = h; }
+  void setDimensions(int w, int h) { _w = w; _h = h; }
 public:
   enum Color { DARK=0, LIGHT, RED, GREEN, BLUE, YELLOW, ORANGE }; // on b/w screen, colors will be !=0 synonym of light
 
@@ -196,5 +197,6 @@ public:
   }
   
   virtual void setBrightness(uint8_t level) { }  // level 0-4 (min to max), no-op default
+  virtual void setDisplayRotation(uint8_t rot) { }  // 0-3, no-op for fixed-orientation displays
   virtual void endFrame() = 0;
 };

src/helpers/ui/GxEPDDisplay.cpp

@@ -150,6 +150,12 @@ uint16_t GxEPDDisplay::getTextWidth(const char* str) {
   return w;
 }
 
+void GxEPDDisplay::setDisplayRotation(uint8_t rot) {
+  display.setRotation(rot & 3);
+  setDimensions(display.width(), display.height());
+  last_display_crc_value = -1;  // force redraw on next endFrame
+}
+
 void GxEPDDisplay::endFrame() {
   uint32_t crc = display_crc.finalize();
   if (crc != last_display_crc_value) {

src/helpers/ui/GxEPDDisplay.h

@@ -84,5 +84,6 @@ public:
   void drawRect(int x, int y, int w, int h) override;
   void drawXbm(int x, int y, const uint8_t* bits, int w, int h) override;
   uint16_t getTextWidth(const char* str) override;
+  void setDisplayRotation(uint8_t rot) override;
   void endFrame() override;
 };