refactor: split monolithic integration tests into numbered per-area files

Split the 1544-line Integration.Tests.ps1 into 18 focused test files
with numeric prefixes for execution ordering.

New shared helper (_IntegrationHelper.ps1):
- Credential-based auth (root@pam) instead of API tokens
- Skip helpers for env var checks
- Resource discovery (Find-TestVm) for cross-file dependencies
- Register-TestResource for env-var state passing between files

Files created:
  00_Connection, 01_Nodes, 02_Users, 03_Storage, 03a_SharedStorage,
  04_Network, 05_SDN, 06_VMs, 07_Snapshots, 08_Templates,
  09_CloudInit, 10_Containers, 11_LinuxVM, 12_OVA, 13_Firewall,
  14_Backup, 15_Tasks, 99_Cleanup

Key changes:
- All tests use root@pam credentials (not API tokens)
- Each file self-contained with own BeforeAll/AfterAll cleanup
- Token CRUD tests now idempotent (remove-before-create)
- 99_Cleanup is safety-net for any leftover pester-* resources
- SharedStorage renamed to 03a_SharedStorage

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

tests/PSProxmoxVE.Tests/Integration/01_Nodes.Tests.ps1

@@ -0,0 +1,29 @@
+#Requires -Module Pester
+
+BeforeAll {
+    . $PSScriptRoot/_IntegrationHelper.ps1
+    Connect-TestPve
+}
+
+AfterAll {
+    Disconnect-TestPve
+}
+
+Describe 'Nodes — Integration' -Tag 'Integration' {
+    Context 'Nodes' {
+        It 'Should list nodes' {
+            if (Skip-IfNoTarget) { return }
+
+            $nodes = Get-PveNode
+            $nodes | Should -Not -BeNullOrEmpty
+        }
+
+        It 'Should get node status' {
+            if (Skip-IfNoTarget) { return }
+
+            $status = Get-PveNodeStatus -Node $script:Node
+            $status            | Should -Not -BeNullOrEmpty
+            $status.Node       | Should -Be $script:Node
+        }
+    }
+}