truma_inetbox: implement master mode auto-discovery and device scanning

udp_lin_receiver: add option to suppress repeated identical messages

components/truma_inetbox/TrumaiNetBoxApp.cpp

@@ -30,6 +30,14 @@ void TrumaiNetBoxApp::update() {
   this->heater_.update();
   this->timer_.update();
 
+  // Master mode auto-discovery (start device discovery once)
+  if (this->master_mode_ && !this->master_discovery_started_) {
+    this->master_discovery_started_ = true;
+    // Start device discovery for typical Truma heater NAD range
+    this->master_scan_b2(0x7F, 0x00, 0xFF);  // Broadcast scan, full identifier range
+    ESP_LOGI(TAG, "Master mode: Started automatic device discovery");
+  }
+
     // Master TX scheduler (throttle to ~20ms spacing)
   if (this->master_mode_ && !this->master_tx_queue_.empty()) {
     uint32_t now = micros();

components/truma_inetbox/TrumaiNetBoxApp.h

@@ -93,6 +93,7 @@ class TrumaiNetBoxApp : public LinBusProtocol {
   struct MasterReq { uint8_t pid; uint8_t len; uint8_t data[9]; };
   std::queue<MasterReq> master_tx_queue_;
   uint32_t last_master_send_us_ = 0;
+  bool master_discovery_started_ = false;
 
 };