feat(dist): add Windows PowerShell installer (install.ps1)

The `irm … | iex` one-liner for Windows, mirroring install.sh: detect arch,
pull the matching bundle from Releases, extract to %LOCALAPPDATA%\codegraph,
add it to user PATH. Re-run to upgrade. (Windows bundle production in
build-bundle.sh is still TODO.)

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

install.ps1

@@ -0,0 +1,59 @@
+# CodeGraph standalone installer for Windows (PowerShell).
+#
+# Downloads a self-contained bundle (a vendored Node runtime + the app) from
+# GitHub Releases. No Node.js, no build tools required.
+#
+#   irm https://raw.githubusercontent.com/colbymchenry/codegraph/main/install.ps1 | iex
+#
+# Re-run to upgrade. To uninstall: remove $env:LOCALAPPDATA\codegraph and drop
+# its \current\bin entry from your user PATH.
+#
+# Environment:
+#   CODEGRAPH_VERSION      release tag to install (default: latest)
+#   CODEGRAPH_INSTALL_DIR  install location (default: %LOCALAPPDATA%\codegraph)
+
+$ErrorActionPreference = 'Stop'
+$repo = 'colbymchenry/codegraph'
+$installDir = if ($env:CODEGRAPH_INSTALL_DIR) { $env:CODEGRAPH_INSTALL_DIR } else { Join-Path $env:LOCALAPPDATA 'codegraph' }
+
+# 1. Detect architecture -> target matching the release archives.
+$arch = if ([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture -eq 'Arm64') { 'arm64' } else { 'x64' }
+$target = "win32-$arch"
+
+# 2. Resolve the version (latest release unless pinned).
+$version = $env:CODEGRAPH_VERSION
+if (-not $version) {
+  $version = (Invoke-RestMethod "https://api.github.com/repos/$repo/releases/latest").tag_name
+}
+if (-not $version) { throw "codegraph: could not resolve latest version; set CODEGRAPH_VERSION." }
+
+# 3. Download + extract the bundle into a stable 'current' dir (overwritten on upgrade).
+$url = "https://github.com/$repo/releases/download/$version/codegraph-$target.zip"
+Write-Host "Installing CodeGraph $version ($target)..."
+$tmp = Join-Path $env:TEMP ("cg-" + [guid]::NewGuid().ToString())
+New-Item -ItemType Directory -Force -Path $tmp | Out-Null
+$zip = Join-Path $tmp 'cg.zip'
+Invoke-WebRequest -Uri $url -OutFile $zip
+
+$dest = Join-Path $installDir 'current'
+if (Test-Path $dest) { Remove-Item -Recurse -Force $dest }
+New-Item -ItemType Directory -Force -Path $dest | Out-Null
+Expand-Archive -Path $zip -DestinationPath $dest -Force
+# Archives contain a top-level codegraph-<target>\ dir; flatten it.
+$inner = Join-Path $dest "codegraph-$target"
+if (Test-Path $inner) {
+  Get-ChildItem -Force $inner | Move-Item -Destination $dest -Force
+  Remove-Item -Recurse -Force $inner
+}
+Remove-Item -Recurse -Force $tmp
+
+# 4. Put the launcher dir on the user's PATH.
+$binDir = Join-Path $dest 'bin'
+$userPath = [Environment]::GetEnvironmentVariable('Path', 'User')
+if (($userPath -split ';') -notcontains $binDir) {
+  [Environment]::SetEnvironmentVariable('Path', "$binDir;$userPath", 'User')
+  Write-Host "Added $binDir to your PATH (restart your terminal to pick it up)."
+}
+
+Write-Host "Installed to $dest"
+Write-Host "Run: codegraph --help"