feat(test): add Alpine guest-agent VM for ACPI and template tests

Infrastructure:
- build-test-image.sh: Downloads Alpine cloud image, uses virt-customize
  to install qemu-guest-agent, caches at /opt/pve-images/
- prepare-test-vm.sh: SCPs image to nested PVE, creates VM via
  qm importdisk with cloud-init and agent enabled, waits for agent

Workflow:
- Build Alpine image step (cached on runner, only built once)
- Deploy test VM step after provisioning, passes LINUX_VMID to tests

Tests:
- Guest Agent VM lifecycle: verify running, ACPI restart, ACPI stop
- Templates: convert Linux VM to template, clone from template
  (New-PveTemplate, New-PveVmFromTemplate)
- Fix Get-PveTask: use .Upid property instead of whole PveTask object

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

.github/workflows/integration-tests.yml

@@ -176,6 +176,27 @@ jobs:
             exit 1
           fi
 
+      # ── Prepare test Linux VM ──────────────────────────────────────────
+
+      - name: Build Alpine test image (cached)
+        if: inputs.skip_provision != true
+        shell: bash
+        run: |
+          bash ${SCRIPTS_DIR}/build-test-image.sh /opt/pve-images/alpine-guest-agent.qcow2
+
+      - name: Deploy test Linux VM to nested PVE
+        if: inputs.skip_provision != true
+        id: linux_vm
+        shell: bash
+        run: |
+          OUTPUT=$(bash ${SCRIPTS_DIR}/prepare-test-vm.sh \
+            "${{ steps.provision.outputs.host }}" \
+            "${PVE_PASSWORD}" \
+            "/opt/pve-images/alpine-guest-agent.qcow2" \
+            200)
+          LINUX_VMID=$(echo "$OUTPUT" | grep "^LINUX_VMID=" | cut -d= -f2)
+          echo "linux_vmid=${LINUX_VMID}" >> "$GITHUB_OUTPUT"
+
       # ── Build and test ─────────────────────────────────────────────────
 
       - name: Build module
@@ -209,6 +230,7 @@ jobs:
           PVETEST_STORAGE: ${{ steps.target.outputs.storage }}
           PVETEST_ISO_PATH: ${{ runner.temp }}/pvetest.iso
           PVETEST_PVE_VERSION: ${{ matrix.pve_version }}
+          PVETEST_LINUX_VMID: ${{ steps.linux_vm.outputs.linux_vmid }}
         run: |
           Import-Module Pester -MinimumVersion 5.0
           $config = New-PesterConfiguration