fix(template): Fix Git skip path + 7-Zip PATH injection

Two root causes:
1. Git skip check used C:\BuildTools\Git but Git installs to
   C:\Program Files\Git (default). Changed $gitDir to correct path.

2. 7-Zip MSI does not register in system PATH. Registry refresh
   (GetEnvironmentVariable Machine+User) was picking up empty result.
   Fixed: inject sevenZipDir directly into $env:PATH if not present.

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

template/Setup-WinBuild2025.ps1

@@ -991,7 +991,7 @@ if (-not (Test-Path $buildToolsRoot)) {
 }
 
 # ── Git for Windows ───────────────────────────────────────────────────────────
-$gitDir = Join-Path $buildToolsRoot 'Git'
+$gitDir = 'C:\Program Files\Git'   # default install location for Git for Windows
 $gitExe = Join-Path $gitDir 'bin\git.exe'
 
 if (Test-Path $gitExe) {
@@ -1079,9 +1079,10 @@ if (Test-Path $sevenZipExe) {
     Write-Host "7-Zip installed."
 }
 
-# Refresh PATH whether freshly installed or already present
-$env:PATH = [System.Environment]::GetEnvironmentVariable('PATH', 'Machine') + ';' +
-            [System.Environment]::GetEnvironmentVariable('PATH', 'User')
+# 7-Zip MSI does NOT add to system PATH — inject directory directly
+if ($env:PATH -notlike "*$sevenZipDir*") {
+    $env:PATH = $env:PATH + ";$sevenZipDir"
+}
 
 # Validation
 Assert-Step '7-Zip' '7z.exe exists at expected path' {