feat(gateway): add support for KNX TP UART 9-bit mode and enhance UART pin configuration

Signed-off-by: Tony <tonylu@tony-cloud.com>

apps/gateway/main/Kconfig.projbuild

@@ -772,6 +772,16 @@ config GATEWAY_KNX_TP_BAUDRATE
     range 1200 921600
     default 19200
 
+config GATEWAY_KNX_TP_UART_9BIT_MODE
+    bool "KNX TP UART 9-bit mode"
+    depends on GATEWAY_KNX_BRIDGE_SUPPORTED
+    default y
+    help
+        Enable the NCN5120/OpenKNX-style 9-bit UART frame on the wire. ESP-IDF
+        exposes this as 8 data bits plus even parity, matching the TP-UART host
+        mode commonly described as 19200 baud 9-bit UART. Disable only for
+        hardware wired for 8N1 host UART mode.
+
 config GATEWAY_BRIDGE_KNX_TASK_STACK_SIZE
     int "KNX/IP bridge task stack bytes"
     depends on GATEWAY_KNX_BRIDGE_SUPPORTED

apps/gateway/main/app_main.cpp

@@ -886,6 +886,11 @@ extern "C" void app_main(void) {
       default_knx.tp_uart.tx_pin = CONFIG_GATEWAY_KNX_TP_TX_PIN;
       default_knx.tp_uart.rx_pin = CONFIG_GATEWAY_KNX_TP_RX_PIN;
       default_knx.tp_uart.baudrate = static_cast<uint32_t>(CONFIG_GATEWAY_KNX_TP_BAUDRATE);
+    #ifdef CONFIG_GATEWAY_KNX_TP_UART_9BIT_MODE
+      default_knx.tp_uart.nine_bit_mode = true;
+    #else
+      default_knx.tp_uart.nine_bit_mode = false;
+    #endif
       bridge_config.default_knx_config = default_knx;
     }
     bridge_config.knx_task_stack_size =