Add Adalight serial LED device support with per-type discovery and capability-based UI

Implements the second device provider (Adalight) for Arduino-based serial LED controllers,
validating the LEDDeviceProvider abstraction. Adds serial port auto-discovery, per-type
discovery caching with lazy-load, capability-driven UI (brightness control, manual LED count,
standby), and serial port combobox in both Add Device and General Settings modals.

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

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

@@ -102,12 +102,16 @@
   "devices.wled_note_webui": "(open your device's IP in a browser).",
   "devices.wled_note2": "This controller sends pixel color data and controls brightness per device.",
   "device.scan": "Auto Discovery",
-  "device.scan.empty": "No WLED devices found on the network",
+  "device.scan.empty": "No devices found",
   "device.scan.error": "Network scan failed",
   "device.scan.already_added": "Already added",
   "device.scan.selected": "Device selected",
   "device.type": "Device Type:",
   "device.type.hint": "Select the type of LED controller",
+  "device.serial_port": "Serial Port:",
+  "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.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",