Initial implementation of BLE-to-TCP serial bridge for Android

Android app that connects to a BLE UART device (Nordic UART Service by
default, matching RNode BLE) and exposes it as a TCP byte pipe, so socat
can present it to Reticulum as a serial port. Foreground service hosts a
GATT client with MTU negotiation, chunked serialized writes, and
auto-reconnect, plus a single-client last-wins TCP server. No root
required on either end.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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+.gradle/
+build/
+local.properties
+.idea/
+.vscode/
+*.iml
+.DS_Store
+.kotlin/