mbproxy/install: add Windows service-management batch files

Four simple .bat files — install / remove / start / stop-service — that
manage the 'mbproxy' Windows service against the Mbproxy.exe in their
own folder. publish.ps1 / publish.sh copy them into each win-* publish
flavour, so a published Windows folder is self-managing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mbproxy/install/start-service.bat

@@ -0,0 +1,15 @@
+@echo off
+REM ---------------------------------------------------------------------------
+REM Starts the "mbproxy" Windows service. Run this script as Administrator.
+REM ---------------------------------------------------------------------------
+setlocal
+
+net session >nul 2>&1
+if errorlevel 1 (
+    echo ERROR: this script must be run as Administrator.
+    pause
+    exit /b 1
+)
+
+net start mbproxy
+pause