refactor: use try/finally for Push-Location cleanup

Ensures Pop-Location is always called, even if Write-Err exits early.
Makes the cleanup pattern consistent and easier to maintain.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/install-core.ps1

@@ -55,12 +55,14 @@ function Build-FromSource {
 
         Write-Info "Building core CLI..."
         Push-Location $cloneDir
+        try {
             go build -o core.exe .
             if ($LASTEXITCODE -ne 0) {
-            Pop-Location
                 Write-Err "Go build failed"
             }
+        } finally {
             Pop-Location
+        }
 
         New-Item -ItemType Directory -Force -Path $InstallDir | Out-Null
         Move-Item (Join-Path $cloneDir "core.exe") (Join-Path $InstallDir "core.exe") -Force