feat: stream build output in real-time + log capture and retention

Invoke-RemoteBuild.ps1:
- Custom build command: replace buffered collect-then-print with
  Write-Host streaming inside Invoke-Command (WinRM forwards Write-Host
  in real-time to the host console)
- Set PYTHONUNBUFFERED=1 in the remote session to prevent Python from
  holding lines in its internal buffer
- Same streaming approach for dotnet restore and dotnet build paths
- Return value is now just int exit code instead of hashtable

Invoke-CIJob.ps1:
- Add -LogDir parameter (default F:\CI\Logs)
- Add -LogRetentionDays parameter (default 30)
- Start-Transcript at job start -> F:\CI\Logs\<JobId>\invoke-ci.log
- Stop-Transcript in finally block (guaranteed execution)
- Auto-purge log directories older than LogRetentionDays after each job

scripts/Invoke-CIJob.ps1

@@ -108,7 +108,15 @@ param(
 
     [string] $GuestCredentialTarget = 'BuildVMGuest',
 
-    [string] $VmrunPath = 'C:\Program Files (x86)\VMware\VMware Workstation\vmrun.exe'
+    [string] $VmrunPath = 'C:\Program Files (x86)\VMware\VMware Workstation\vmrun.exe',
+
+    # Directory for job execution logs. Each job gets its own sub-directory:
+    # $LogDir\$JobId\invoke-ci.log
+    [string] $LogDir = 'F:\CI\Logs',
+
+    # Days to retain job logs. Directories older than this are purged at job end.
+    # Set to 0 to disable retention/purge.
+    [int] $LogRetentionDays = 30
 )
 
 Set-StrictMode -Version Latest
@@ -152,6 +160,19 @@ $hostCloneDir   = Join-Path $env:TEMP "ci-src-$JobId"
 $cloneVmxPath   = $null
 $startTime      = Get-Date
 
+# ── Start transcript ──────────────────────────────────────────────────────────
+$transcriptStarted = $false
+try {
+    $jobLogDir = Join-Path $LogDir $JobId
+    if (-not (Test-Path $jobLogDir)) { New-Item -ItemType Directory -Path $jobLogDir -Force | Out-Null }
+    $transcriptPath = Join-Path $jobLogDir 'invoke-ci.log'
+    Start-Transcript -Path $transcriptPath -Force -ErrorAction Stop
+    $transcriptStarted = $true
+}
+catch {
+    Write-Warning "[Invoke-CIJob] Could not start transcript: $_"
+}
+
 Write-Host "============================================================"
 Write-Host "[Invoke-CIJob] Job          : $JobId"
 Write-Host "[Invoke-CIJob] Repository   : $RepoUrl"
@@ -276,6 +297,22 @@ finally {
         Write-Host "[Cleanup] Removing host source clone ($hostCloneDir)..."
         Remove-Item $hostCloneDir -Recurse -Force -ErrorAction SilentlyContinue
     }
+
+    # ── Stop transcript ───────────────────────────────────────────────────
+    if ($transcriptStarted) {
+        try { Stop-Transcript -ErrorAction SilentlyContinue } catch {}
+    }
+
+    # ── Log retention: purge directories older than $LogRetentionDays days ─
+    if ($LogRetentionDays -gt 0 -and (Test-Path $LogDir)) {
+        $cutoff = (Get-Date).AddDays(-$LogRetentionDays)
+        Get-ChildItem -Path $LogDir -Directory -ErrorAction SilentlyContinue |
+            Where-Object { $_.LastWriteTime -lt $cutoff } |
+            ForEach-Object {
+                Remove-Item $_.FullName -Recurse -Force -ErrorAction SilentlyContinue
+                Write-Host "[Cleanup] Purged old log dir: $($_.FullName)"
+            }
+    }
 }
 
 exit $exitCode