Add XIAO Wio-SX1262 overlay; support SX12xx bandwidths (including 62.5 kHz) as default

- boards/seeed/xiao_wio_sx1262: add overlay, .conf, board.yml
- app: support full set of SX12xx bandwidths; default BW set to 62 (62.5 kHz)
- Update Kconfig and prj.conf
- Update lora_modem.h/c for validation and mapping

boards/lilygo/lilygo_tbeam/board.yml

@@ -2,7 +2,6 @@ board:
   name: lilygo_tbeam
   full_name: "LilyGo T-Beam"
   vendor: lilygo
-  url: https://www.lilygo.cc/products/t-beam-v1-1
   socs:
     - name: esp32
       variants:

boards/lilygo/ttgo_lora32.conf

@@ -0,0 +1,7 @@
+# LilyGO TTGO LoRa32 — ESP32 + SX127x
+# Uses hardware UART over onboard USB-Serial bridge
+
+CONFIG_LORAMODEM_KISS_IFACE_UART=y
+
+# SX127x driver (via loramac-node)
+CONFIG_LORA_SX12XX=y

boards/lilygo/ttgo_lora32.overlay

@@ -0,0 +1,11 @@
+/*
+ * LilyGO TTGO LoRa32 — application DTS overlay
+ * KISS interface: UART0 (via onboard USB-Serial bridge)
+ * LoRa: SX127x on SPI (assumed present in upstream board DTS)
+ */
+
+/ {
+	chosen {
+		loramodem,kiss-uart = &uart0;
+	};
+};