fix: address Copilot review round 3

- Fix bare Skip-IfNoTarget calls in 13_Firewall and 14_Backup
  (missing if/return pattern caused tests to run when they should skip)
- Validate modifier-only switches in dev.ps1 (-Force/-Reprovision
  without an action switch now errors instead of defaulting to -Shell)
- Add force-cleanup to usage text in run-integration.sh
- Add --connect-timeout/--max-time to guest agent curl in wait-for-pve.sh

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/dev.ps1

@@ -114,9 +114,12 @@ param(
 
 $ErrorActionPreference = 'Stop'
 
-# If no switches specified, default to -Shell
+# If no action switches specified, default to -Shell
 $anySwitchSet = $Shell -or $Build -or $Test -or $Provision -or $Integration -or $Cleanup -or $Stop -or $Rebuild
 if (-not $anySwitchSet) {
+    if ($Force -or $Reprovision) {
+        throw "-Force and -Reprovision are modifiers — combine with an action switch (e.g. -Cleanup -Force, -Provision -Reprovision)."
+    }
     $Shell = $true
 }