merge: upstream/dev into observer-firmware-dev (2026-07-30, db232808)

Absorbs 106 upstream commits. Seven files conflicted; the substantive one
was upstream's new JSON ConfigSerializer (PR #2982), which replaces the
binary /com_prefs layout with /prefs.json and makes NodePrefs a
ConfigSerializer subclass.

Prefs migration
- Adopt upstream's ConfigSerializer. writeCommonPrefsImage() and its
  documented offsets (0-294) are deleted, along with the now-unreachable
  saveCommonPrefsImageAtomically()/CommonPrefsFileStore atomic rename path.
- Load order is /prefs.json, then /com_prefs, then /node_prefs. Upstream
  dropped the /node_prefs fallback; it is restored here so devices that
  never advanced past that filename keep their config.
- Legacy files are never removed, so migration cannot destroy its own
  source and a deferred or failed save simply retries next boot.
- /com_prefs is treated as a format migration only, not an "upgrade", so
  it does not trip the bridge.source tx->rx flip on existing nodes.
- The MQTTPrefsAtomicStore legacy gate is retained: the observer tail
  recovered from an old-format file still commits to /mqtt_prefs before
  /prefs.json is written.
- MQTTPrefs and /mqtt_prefs are untouched; savePrefs keeps its save_mqtt
  parameter and now returns upstream's bool.

Fixes to upstream code
- RadioPrefs::structure() bound both "rxgain" and "fem_rxgain" to
  rx_boosted_gain, so radio_fem_rxgain was never persisted. Bound to the
  correct field.
- discovery_mod_timestamp was dropped from structure(); it gates
  'since'-filtered DISCOVER replies and is set on every config change, so
  losing it would silently stop discovery responses after a reboot. Added
  as "disc_mod".

Merge artifacts repaired
- Restored bblanchon/ArduinoJson to the native test env; a clean but wrong
  auto-merge at the lib_deps block boundary dropped it and broke all 19
  host test suites.
- Migrated the fork's WebConfig UITask screens off the removed
  DisplayDriver::Color enum to upstream's UIColor element types.
- Removed duplicate getCADEnabled() definitions in companion MyMesh.cpp
  and simple_sensor SensorMesh.cpp that both sides had added.
- Dropped memset(&_prefs, 0, ...) in the four example meshes; NodePrefs now
  has a vtable. guard gains an initializer that memset used to provide.

Other resolutions
- simple_room_server keeps both the fork's discover.* commands and
  upstream's new room.post.
- docs/payloads.md taken from upstream, undoing content earlier merges had
  reverted (Control data section, split login tables).

Verified: 273/273 host tests pass across native and native_kiss_modem;
Heltec v3 repeater, repeater_observer_mqtt, room_server_observer_mqtt,
sensor, and companion_radio_ble all build clean.

src/helpers/ui/ST7735Display.cpp

@@ -421,6 +421,17 @@ bool ST7735Display::i2c_probe(TwoWire& wire, uint8_t addr) {
   #define PIN_TFT_LEDA_CTL_ACTIVE  HIGH
 #endif
 
+// Color scheme
+ColorVal UIColor::window_bkg = ST77XX_WHITE;
+ColorVal UIColor::title_bkg = ST77XX_BLUE;
+ColorVal UIColor::title_txt = ST77XX_WHITE;
+ColorVal UIColor::primary_txt = ST77XX_BLACK;
+ColorVal UIColor::secondary_txt = (18 << 11) | (36 << 5) | 18;  // mid-gray
+ColorVal UIColor::warning_txt = ST77XX_ORANGE;
+ColorVal UIColor::popup_bkg = ST77XX_CYAN;
+ColorVal UIColor::popup_txt = ST77XX_BLACK;
+ColorVal UIColor::corp_blue = 0x001A;
+
 bool ST7735Display::begin() {
   if (!sprite) {
     // alloc offscreen canvas
@@ -531,9 +542,9 @@ void ST7735Display::clear() {
   sprite->fillScreen(ST77XX_BLACK);
 }
 
-void ST7735Display::startFrame(Color bkg) {
-  sprite->fillScreen(ST77XX_BLACK);
-  sprite->setTextColor(curr_color = ST77XX_WHITE);
+void ST7735Display::startFrame(ColorVal bkg) {
+  sprite->fillScreen(bkg);
+  sprite->setTextColor(curr_color = UIColor::primary_txt);
   sprite->setFreeFont();
   sprite->setTextSize(1);      // This one affects size of Please wait... message
   //sprite->cp437(true);         // Use full 256 char 'Code Page 437' font
@@ -543,33 +554,8 @@ void ST7735Display::setTextSize(int sz) {
   sprite->setTextSize(sz);
 }
 
-void ST7735Display::setColor(Color c) {
-  switch (c) {
-    case DisplayDriver::DARK :
-      curr_color = ST77XX_BLACK;
-      break;
-    case DisplayDriver::LIGHT : 
-      curr_color = ST77XX_WHITE;
-      break;
-    case DisplayDriver::RED : 
-      curr_color = ST77XX_RED;
-      break;
-    case DisplayDriver::GREEN : 
-      curr_color = ST77XX_GREEN;
-      break;
-    case DisplayDriver::BLUE : 
-      curr_color = ST77XX_BLUE;
-      break;
-    case DisplayDriver::YELLOW : 
-      curr_color = ST77XX_YELLOW;
-      break;
-    case DisplayDriver::ORANGE : 
-      curr_color = ST77XX_ORANGE;
-      break;
-    default:
-      curr_color = ST77XX_WHITE;
-      break;
-  }
+void ST7735Display::setColor(ColorVal c) {
+  curr_color = c;
   sprite->setTextColor(curr_color);
 }