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/pyproject.toml

@@ -38,6 +38,7 @@ dependencies = [
     "python-multipart>=0.0.12",
     "wmi>=1.5.1; sys_platform == 'win32'",
     "zeroconf>=0.131.0",
+    "pyserial>=3.5",
 ]
 
 [project.optional-dependencies]