test: expand integration and unit test coverage to 84 test cases

Integration tests (27 contexts, 84 test cases, up from 48 cmdlets to 76):
- VM: Suspend/Resume/Resize
- Containers: full lifecycle (create, config, start, stop, restart, clone)
- Container Snapshots: create, list, restore, remove
- SDN: zone/vnet/subnet CRUD (PVE 8+ version-gated)
- Storage: create/remove directory storage, Invoke-PveStorageDownload
- OVA Import: Import-PveOva with generated test OVA
- Cloud-Init: Invoke-PveCloudInitRegenerate
- Templates: Remove-PveTemplate
- Disconnect-PveServer: verify disconnect + post-disconnect failure

Unit tests:
- Guest agent cmdlets (Test-PveVmGuestAgent, Get-PveVmGuestNetwork,
  Invoke-PveVmGuestExec) — parameter metadata, ShouldProcess, session

Test infrastructure:
- prepare-test-environment.sh generates minimal test OVA (OVF + 1MB VMDK)
- CI workflow passes PVETEST_OVA_PATH to integration tests

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

.github/workflows/integration-tests.yml

@@ -285,7 +285,9 @@ jobs:
             "${PVE_PASSWORD}" \
             "${RUNNER_TEMP}")
           CLOUD_IMAGE_PATH=$(echo "$OUTPUT" | grep "^CLOUD_IMAGE_PATH=" | cut -d= -f2)
+          OVA_PATH=$(echo "$OUTPUT" | grep "^OVA_PATH=" | cut -d= -f2)
           echo "cloud_image_path=${CLOUD_IMAGE_PATH}" >> "$GITHUB_OUTPUT"
+          echo "ova_path=${OVA_PATH}" >> "$GITHUB_OUTPUT"
 
       # ── Run tests ─────────────────────────────────────────────────────
 
@@ -304,6 +306,7 @@ jobs:
           PVETEST_PVE_VERSION: ${{ matrix.pve_version }}
           PVETEST_PASSWORD: ${{ env.PVE_PASSWORD }}
           PVETEST_CLOUD_IMAGE_PATH: ${{ steps.test_env.outputs.cloud_image_path }}
+          PVETEST_OVA_PATH: ${{ steps.test_env.outputs.ova_path }}
         run: |
           $env:PVETEST_ISO_PATH = Join-Path $env:RUNNER_TEMP "pvetest.iso"
           Import-Module Pester -MinimumVersion 5.0