feat(medium): sprint 3 Medium items 6 implementati, 6 confermati gia' presenti

codice:
- Watch-DiskSpace.ps1: Event Log source CI-DiskAlert -> CI-DiskSpaceAlert
  (allineato con task scheduler CI-DiskSpaceAlert)
- Watch-RunnerHealth.ps1: maintenance flag  salta restart se
  F:\CI\State\runner-maintenance.flag esiste
- Invoke-CIJob.ps1:
  - param WebhookUrl (default '') per alert webhook
  - sanity check TemplatePath: Write-Warning se non sotto F:\CI\Templates\
  - 90-min duration warning: Start-Job che posta [WARNING] dopo 5400s
  - finally: Remove-Job per cancellare il warn se build finisce prima

docs:
- BEST-PRACTICES.md sezione 11: VMware HGFS write semantics e cache-poisoning risk
- final-master-plan.md: marcati done  post-failure diagnostics, UseSharedCache,
  VMDK SHA256, SSH host-key, template-refresh runbook, 90-min warn, HGFS,
  Event Log names, TemplatePath sanity, maintenance flag, Setup-Host pass docs,
  emoji-free webhooks

scripts/Watch-RunnerHealth.ps1

@@ -85,6 +85,15 @@ function Send-Webhook {
     }
 }
 
+# ── Maintenance flag check ────────────────────────────────────────────────────
+# If F:\CI\State\runner-maintenance.flag exists, skip all restart logic.
+# Create the flag before planned maintenance; delete it when done.
+$maintenanceFlag = Join-Path $StateDir 'runner-maintenance.flag'
+if (Test-Path $maintenanceFlag) {
+    Write-Host "[RunnerHealth] Maintenance mode active (flag: $maintenanceFlag) — skipping restart logic."
+    exit 0
+}
+
 # ── Step 1: Check service ─────────────────────────────────────────────────────
 $svc = Get-Service -Name $ServiceName -ErrorAction SilentlyContinue
 if (-not $svc) {