Add configurable baud rate for Adalight with dynamic FPS hint

Baud rate is now a first-class device field, passed through the full
stack: Device model → API schemas → routes → ProcessorManager →
AdalightClient. The frontend shows a baud rate dropdown (115200–2M)
for Adalight devices in both Add Device and Settings modals, with a
live "Max FPS ≈ N" hint computed from LED count and baud rate.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/locales/en.json

@@ -112,6 +112,8 @@
   "device.serial_port.hint": "Select the COM port of the Adalight device",
   "device.serial_port.none": "No serial ports found",
   "device.led_count_manual.hint": "Number of LEDs on the strip (must match your Arduino sketch)",
+  "device.baud_rate": "Baud Rate:",
+  "device.baud_rate.hint": "Serial communication speed. Higher = more FPS but requires matching Arduino sketch.",
   "device.url.hint": "IP address or hostname of the device (e.g. http://192.168.1.100)",
   "device.name": "Device Name:",
   "device.name.placeholder": "Living Room TV",