Add mock LED device type for testing without hardware

Virtual device with configurable LED count, RGB/RGBW mode, and simulated
send latency. Includes full provider/client implementation, API schema
support, and frontend add/settings modal integration.

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

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

@@ -122,6 +122,10 @@
   "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.led_type": "LED Type:",
+  "device.led_type.hint": "RGB (3 channels) or RGBW (4 channels with dedicated white)",
+  "device.send_latency": "Send Latency (ms):",
+  "device.send_latency.hint": "Simulated network/serial delay per frame in milliseconds",
   "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",