fix: address Copilot review — validation, error handling, MAC case

- Add ValidateSet('8','9','all') to dev.ps1 -Version parameter
- Fix Shell warning to reference $DevContainer not $InfraContainer
- Fix Skip-IfNoNodeB to check $PasswordB not $Password
- Pass PVE_TARGET_NODE to wait-for-pve.sh instead of auto-discovering
- Add error default cases to all pve_* helper functions
- Lowercase MAC addresses for answer server matching
- Create answer file paths before terraform destroy in cleanup

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

tests/PSProxmoxVE.Tests/Integration/_IntegrationHelper.ps1

@@ -81,7 +81,7 @@ function script:Skip-IfNoOva {
 
 function script:Skip-IfNoNodeB {
     if (Skip-IfNoTarget) { return $true }
-    if (-not $script:HostB -or -not $script:Password) {
+    if (-not $script:HostB -or -not $script:PasswordB) {
         Set-ItResult -Skipped -Because 'Multi-node env vars not set (PVETEST_HOST_B, PVETEST_PASSWORD)'
         return $true
     }