Add Windows Terminal installer (install.ps1 / install.bat)

install.ps1 copies bash.exe to %LOCALAPPDATA%\Programs\BashForWindows,
adds it to the user PATH, and injects a "Bash for Windows" profile into
Windows Terminal's settings.json so the shell appears in the + dropdown.

install.bat is a double-click wrapper that bypasses the PS execution policy.

build.sh --release produces a release/ folder ready to zip and distribute.
Supports -Uninstall flag to cleanly remove everything.

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

install.bat

@@ -0,0 +1,19 @@
+@echo off
+setlocal
+
+REM Run the PowerShell installer from the same directory as this .bat file.
+REM Works even if PowerShell's execution policy is Restricted.
+
+echo.
+echo  bash-for-windows installer
+echo.
+
+powershell.exe -NoProfile -ExecutionPolicy Bypass ^
+    -File "%~dp0install.ps1" %*
+
+if %ERRORLEVEL% NEQ 0 (
+    echo.
+    echo  Installation failed. See error above.
+    pause
+    exit /b %ERRORLEVEL%
+)