fix(pvc): handle FileSystemResizePending condition to prevent pod creation deadlock

Closes #9980

Problem

When a PVC has the FileSystemResizePending condition, CloudNativePG incorrectly classifies it as "resizing" even when no pod is attached. This causes a deadlock:

1. PVC resize completes at storage layer
2. Kubernetes adds FileSystemResizePending condition (filesystem resize needs pod mount)
3. Pod is deleted or crashes
4. CloudNativePG sees PVC as "resizing" and does NOT create a new pod
5. Filesystem resize never completes because no pod mounts the volume
6. Cluster is stuck

Root Cause

In classifyPVC(), the resizing check happens before the pod existence check:

// Before (buggy):
if isResizing(pvc) {
    return resizing  // Returns even when no pod exists
}
if hasPod(pvc, podList) {
    return healthy
}

The FileSystemResizePending condition specifically indicates the volume resize is done at the storage layer and requires a pod mount to complete the filesystem resize. Returning resizing prevents pod creation, creating a deadlock.

Solution

Reorder the classification logic to:

1. First check if pod exists - if a pod is attached and resizing, filesystem resize can complete
2. If no pod and FileSystemResizePending - classify as dangling to trigger pod recreation
3. If no pod but only Resizing - classify as resizing (storage resize still in progress)

// After (fixed):
if hasPod(pvc, podList) {
    if isResizing(pvc) {
        return resizing  // Pod attached, resize can complete
    }
    return healthy
}

if isResizing(pvc) {
    if isFileSystemResizePending(pvc) {
        return dangling  // Needs pod to complete filesystem resize
    }
    return resizing  // Storage resize still in progress
}

Changes

• pkg/reconciler/persistentvolumeclaim/resources.go: Add isFileSystemResizePending() helper function
• pkg/reconciler/persistentvolumeclaim/status.go: Reorder classification logic in classifyPVC()
• pkg/reconciler/persistentvolumeclaim/resources_test.go: Add comprehensive tests

Testing

• Unit tests: Added 7 new tests covering:
  • isFileSystemResizePending() function (4 tests)
  • Classification behavior with FileSystemResizePending (3 tests)
• All existing tests pass: 75/75 specs
• Manual verification: Tested resize scenarios on AKS with Azure Disk CSI driver

Compatibility

• Backward compatible: Yes - only changes classification of edge case
• API changes: None
• Backport targets: release-1.28, release-1.27

AI Assistance

This fix was developed with assistance from Claude Opus 4.5 while developing the Dynamic Storage feature. The issue was discovered while running E2E tests on Azure AKS 1.34.2.