Unify Heltec V4 OLED, TFT and headless display selection

Detect OLED or the original stock TFT touch assembly in ordinary V4.2/V4.3
images. Add saved live display.type auto/oled/tft/off selection and report
the active selection in board output. Keep sensors on primary I2C, preserve
shared power, and isolate TFT FSPI from radio HSPI through sleep and changes.

Consolidate future picker/build choices only with application capability
proof. Retain exact legacy OTA identities and separate R8 hardware images.
Document controls and physical qualification limits.

Validation: five serialized Full builds with capability/size/RAM checks;
focused host tests, existing R8/T-Deck/OLED regressions, build-profile suite,
and picker/provider tests. V4.3 OLED live changes and off/auto reboot
persistence passed on Mercerwood. Physical TFT qualification remains pending.

examples/simple_sensor/main.cpp

@@ -5,6 +5,9 @@
 #include <helpers/IdentityGeneration.h>
 #include <helpers/ui/StartupScreen.h>
 #include <helpers/ui/DisplayPowerSettings.h>
+#if defined(HELTEC_V4_DISPLAY_UNIFIED) && HELTEC_V4_DISPLAY_UNIFIED && defined(DISPLAY_CLASS)
+#include <helpers/ui/HeltecV4DisplaySettings.h>
+#endif
 #if defined(OLED_AUTO_DETECT) && OLED_AUTO_DETECT
 #include <helpers/ui/OLEDControllerSettings.h>
 #endif
@@ -179,6 +182,9 @@ void setup() {
   mesh::RadioProfileCLI::configureBootTuning(regulator_prefs_fs, radio_driver);
 #ifdef DISPLAY_CLASS
   mesh::ui::loadDisplayPowerSettings(fs, false);
+#if defined(HELTEC_V4_DISPLAY_UNIFIED) && HELTEC_V4_DISPLAY_UNIFIED
+  mesh::ui::loadHeltecV4DisplaySettings(regulator_prefs_fs, display);
+#endif
 #if defined(OLED_AUTO_DETECT) && OLED_AUTO_DETECT
   mesh::ui::loadOLEDControllerSettings(regulator_prefs_fs);
 #endif
@@ -294,6 +300,11 @@ void setup() {
 #endif
 
 #ifdef DISPLAY_CLASS
+#if defined(HELTEC_V4_DISPLAY_UNIFIED) && HELTEC_V4_DISPLAY_UNIFIED
+  // Initialize the UI dependency even when auto detection found no screen.
+  // A later saved display.type change can enable it without restarting.
+  display_ready = true;
+#endif
   if (display_ready) {
     ui_task.begin(the_mesh.getNodePrefs(), FIRMWARE_BUILD_DATE, FIRMWARE_VERSION);
   }
@@ -376,7 +387,11 @@ void loop() {
   const bool morse_timing = mesh::morseTimingActive(&radio_driver);
   if (!morse_timing) sensors.loop();
 #ifdef DISPLAY_CLASS
+#if defined(HELTEC_V4_DISPLAY_UNIFIED) && HELTEC_V4_DISPLAY_UNIFIED
+  if (display.selectedType() != mesh::ui::HeltecV4DisplayType::None) ui_task.loop();
+#else
   if (display_ready) ui_task.loop();
+#endif
 #endif
   rtc_clock.tick();
   if (mesh::serviceUsbLoggingWatchdog(usbLoggingRecoverySafe)) board.reboot();