Add build script

scripts/build-win.ps1

@@ -0,0 +1,76 @@
+$ErrorActionPreference = 'Stop'
+
+<#
+.SYNOPSIS
+  Build a single-file, no-dependency Windows binary for BgVisionAgent.
+
+.DESCRIPTION
+  Uses PyInstaller to bundle the app and its Python dependencies into a single
+  `BgVisionAgent.exe` suitable for systems without Python installed.
+
+  Run this on Windows with Python 3.11 or 3.12 installed.
+
+.EXAMPLE
+  powershell -ExecutionPolicy Bypass -File scripts\build-win.ps1
+
+.NOTES
+  - Output: dist\BgVisionAgent.exe
+  - You may need to run the resulting EXE as Administrator for global hotkeys.
+  - To publish, copy the EXE to `bin/BgVisionAgent.exe` in this repo (or
+    upload to your hosting and set BG_BINARY_URL accordingly in bootstrap).
+#>
+
+function Assert-Exe($exe) {
+  $exists = Get-Command $exe -ErrorAction SilentlyContinue
+  if (-not $exists) { throw "Required tool not found in PATH: $exe" }
+}
+
+Write-Host "[build] Preparing isolated venv..." -ForegroundColor Cyan
+$root = Split-Path -Parent $MyInvocation.MyCommand.Path
+Set-Location $root
+Set-Location ..
+
+$venv = Join-Path (Get-Location) ".build-venv"
+if (Test-Path $venv) { Remove-Item $venv -Recurse -Force }
+
+try {
+  py -3 -m venv $venv
+} catch {
+  python -m venv $venv
+}
+
+$pip = Join-Path $venv "Scripts/pip.exe"
+$python = Join-Path $venv "Scripts/python.exe"
+
+& $pip install --upgrade pip wheel setuptools | Out-Null
+& $pip install -r requirements.txt | Out-Null
+& $pip install pyinstaller | Out-Null
+
+Write-Host "[build] Running PyInstaller (one-file, windowed)..." -ForegroundColor Cyan
+
+$common = @(
+  "--noconfirm",
+  "--clean",
+  "-F",
+  "-w",
+  "-n","BgVisionAgent",
+  "--collect-all","openai",
+  "--collect-all","pyautogui",
+  "--collect-all","pyscreeze",
+  "--collect-all","mouseinfo",
+  "--collect-all","pymsgbox",
+  "--collect-all","pytweening",
+  "--collect-all","pyperclip",
+  "--collect-all","keyboard",
+  "--collect-all","PIL",
+  "--collect-all","certifi",
+  "--hidden-import","win32api",
+  "--hidden-import","win32gui",
+  "--hidden-import","win32con"
+)
+
+& $python -m PyInstaller @common bg_agent/__main__.py
+
+Write-Host "[build] Done. Binary at: dist\\BgVisionAgent.exe" -ForegroundColor Green
+Write-Host "[build] Tip: copy dist\\BgVisionAgent.exe to bin\\BgVisionAgent.exe for bootstrap downloads." -ForegroundColor DarkGray
+