feat(devices): Android USB-serial support for Adalight/AmbiLED controllers

Adds end-to-end support for driving USB-connected Adalight / AmbiLED
LED controllers from Android TV boxes. Android's security model blocks
direct USB access from Python, so writes route through a Kotlin
UsbSerialBridge singleton via Chaquopy.

Python side:
- New SerialTransport Protocol (serial_transport.py) with open / write /
  flush / close. Desktop uses PySerialTransport (wraps pyserial),
  Android uses AndroidSerialTransport (wraps the Kotlin bridge).
- list_serial_ports() factory returns desktop COM ports on desktop,
  USB devices on Android — callers don't branch.
- URL scheme extended: existing COM3[:baud] and /dev/ttyUSB0[:baud]
  unchanged; new usb:VID:PID[:serial][@baud] for Android (@ is the
  baud separator since : is already used between VID and PID).
- AdalightClient and SerialDeviceProvider refactored to go through
  the transport — no more direct pyserial imports in hot paths.
- 17 new unit tests cover URL parsing, PySerial transport, factory
  selection, platform-branching discovery. Full suite 750 passing.

Kotlin side:
- UsbSerialBridge.kt singleton uses com.hoho.android.usbserial (mik3y)
  which ships drivers for CH340, CP2102, FTDI, Prolific, and CDC-ACM
  (Arduino). Exposes listDevices, open, write, close via @JvmStatic
  for Chaquopy. First open() attempt without permission triggers the
  system USB permission dialog; next call succeeds once user grants.
- usb-serial-for-android is distributed via JitPack — added that repo
  in settings.gradle.kts and the dependency in app/build.gradle.kts.
- AndroidManifest declares uses-feature android.hardware.usb.host
  (required=false so non-USB-host phones still install).
- LedGrabApp.onCreate calls UsbSerialBridge.init(this) so the bridge
  resolves the UsbManager without needing an Activity ref.

Verified: ./gradlew compileDebugKotlin succeeds; off-Android import
of android_serial_transport works. Real-hardware smoke test on a
TV box with a CH340/CP2102/FTDI adapter still pending.

ESP-NOW (espnow_client / espnow_provider) still imports pyserial
directly because it needs bidirectional reads — separate refactor
to extend the transport with read() if that path ever needs Android
USB support.

android/app/src/main/AndroidManifest.xml

@@ -21,6 +21,12 @@
         android:name="android.hardware.touchscreen"
         android:required="false" />
 
+    <!-- USB host — for USB-to-TTL adapters driving Adalight/AmbiLED
+         controllers. required=false so phones without USB host still install. -->
+    <uses-feature
+        android:name="android.hardware.usb.host"
+        android:required="false" />
+
     <application
         android:name=".LedGrabApp"
         android:allowBackup="true"