Max: update build date and firmware version. Add keyboard LED brightness setting (MAX); fix standalone unread counter

Keyboard LED brightness (T-Deck Pro MAX):
Adds a "Keyboard LED" row to Settings (MAX only), below Backlight
Brightness and mirroring it: 5-100% in 5% steps, default 50%. The
both-shifts keyboard backlight toggle previously used a hardcoded PWM
level of 8 (~3%), too dim for some users; it now reads the stored
percentage and maps it to PWM, taking effect on the next toggle.
- NodePrefs.h: new kb_backlight_pct field (5..100, default 50)
- Settingsscreen.h: ROW_KB_BACKLIGHT row plus label/edit handling
- DataStore.cpp: load/save/clamp, appended so existing prefs files stay
  compatible (fall back to 50%)
- main.cpp: toggle uses kb_backlight_pct (percent -> PWM) instead of 8

Standalone unread counter fix:
On standalone builds the home-page MSG count and channel-picker unread
badges never updated, although messages arrived and displayed normally.
ArduinoSerialInterface::isConnected() is hardcoded to return true (a plain
UART has no connection state), so the periodic
setHasConnection(_serial->isConnected()) in MyMesh left hasConnection()
permanently true -- making UITask mark every received message read on
arrival. The same stuck flag also suppressed the DM counter and the
new-message screen wake. Guard the call so only builds with a real
companion (BLE / WiFi / wired SERIAL_RX) derive connection state from the
interface; companion-less builds report not-connected. The core
ArduinoSerialInterface is unchanged, preserving wired-companion behaviour.
- MyMesh.cpp: guard setHasConnection() for companion-less builds

examples/companion_radio/DataStore.cpp

@@ -202,6 +202,10 @@ void DataStore::loadPrefs(NodePrefs& prefs, double& node_lat, double& node_lon)
   if (prefs.backlight_brightness_pct < 5 || prefs.backlight_brightness_pct > 100) {
     prefs.backlight_brightness_pct = 100;
   }
+  // Same treatment for the keyboard LED level (fresh device = memset 0).
+  if (prefs.kb_backlight_pct < 5 || prefs.kb_backlight_pct > 100) {
+    prefs.kb_backlight_pct = 50;
+  }
 }
 
 void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& node_lat, double& node_lon) {
@@ -303,6 +307,9 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
     if (file.read((uint8_t *)&_prefs.backlight_brightness_pct, sizeof(_prefs.backlight_brightness_pct)) != sizeof(_prefs.backlight_brightness_pct)) {
       _prefs.backlight_brightness_pct = 100;  // default: full brightness
     }
+    if (file.read((uint8_t *)&_prefs.kb_backlight_pct, sizeof(_prefs.kb_backlight_pct)) != sizeof(_prefs.kb_backlight_pct)) {
+      _prefs.kb_backlight_pct = 50;  // default: 50%
+    }
 
     // Clamp to valid ranges
     if (_prefs.dark_mode > 1) _prefs.dark_mode = 0;
@@ -318,6 +325,7 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
     }
     if (_prefs.lora_antenna > 1) _prefs.lora_antenna = 0;
     if (_prefs.backlight_brightness_pct < 5 || _prefs.backlight_brightness_pct > 100) _prefs.backlight_brightness_pct = 100;
+    if (_prefs.kb_backlight_pct < 5 || _prefs.kb_backlight_pct > 100) _prefs.kb_backlight_pct = 50;
     // auto_lock_minutes: only accept known options (0, 2, 5, 10, 15, 30)
     {
       uint8_t alm = _prefs.auto_lock_minutes;
@@ -380,6 +388,7 @@ void DataStore::savePrefs(const NodePrefs& _prefs, double node_lat, double node_
     file.write((uint8_t *)_prefs.channel_notif, sizeof(_prefs.channel_notif));                   // 153
     file.write((uint8_t *)&_prefs.lora_antenna, sizeof(_prefs.lora_antenna));                    // 174
     file.write((uint8_t *)&_prefs.backlight_brightness_pct, sizeof(_prefs.backlight_brightness_pct)); // 175
+    file.write((uint8_t *)&_prefs.kb_backlight_pct, sizeof(_prefs.kb_backlight_pct));            // 176
 
     file.close();
   }