[occm] Support instance discovery via system UUID instead of hostname-only matching

## Problem

The current `getServerByName()` implementation in `pkg/openstack/instances.go` discovers OpenStack instances by matching the Kubernetes node name against Nova server names using an exact regex match:

```go
opts := servers.ListOpts{
Name: fmt.Sprintf("^%s$", regexp.QuoteMeta(name)),
}
```

This silently fails when the Kubernetes node hostname does not exactly match the OpenStack instance name — which is common in:

- **RKE2/K3s**: hostnames set via `--node-name` or OS hostname may differ from Terraform resource names
- **Autoscaling**: instance names include random suffixes that don't match kubelet hostnames
- **Enterprise naming**: organizations may have different naming conventions for infra vs K8s

When discovery fails, OCCM sets no `providerID`, no zone/region labels, and logs no error — making this extremely hard to diagnose.

## Proposed Solution

Kubernetes nodes already expose the SMBIOS system UUID via `node.status.nodeInfo.systemUUID`. OpenStack sets the Nova instance UUID as the guest's SMBIOS product UUID, making this a reliable 1:1 mapping.

The `getInstance()` function should try multiple discovery strategies in order:

```go
func (i *InstancesV2) getInstance(ctx context.Context, node *v1.Node) (*servers.Server, error) {
// 1. If providerID already set, use it (existing behavior)
if node.Spec.ProviderID != "" {
return getServerByProviderID(...)
}

// 2. Try system UUID — Nova servers.Get(uuid) — most reliable
if uuid := node.Status.NodeInfo.SystemUUID; uuid != "" {
srv, err := servers.Get(ctx, i.compute, strings.ToLower(uuid)).Extract()
if err == nil {
return srv, nil
}
klog.V(4).Infof("Failed to find instance by system UUID %s: %v, falling back to name match", uuid, err)
}

// 3. Fallback to name match (existing behavior)
return getServerByName(ctx, i.compute, node.Name)
}
```

This is:
- **Zero-config**: No new cloud.conf options needed
- **Backward-compatible**: Falls back to name match if UUID lookup fails
- **Reliable**: SMBIOS UUID = Nova instance UUID is guaranteed by OpenStack

## Evidence

On an RKE2 cluster where node hostnames don't match Nova server names, `systemUUID` correctly maps to the OpenStack instance:

```
$ kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.nodeInfo.systemUUID}{"\n"}{end}'
cpe-central-master-1 0e6d1a84-b37c-40d2-bb69-76f9b22fd5bb
cpe-central-master-2 989ec61a-37e2-4f7a-9927-4833f55be53e
cpe-central-master-3 24038e8a-fa44-45dc-9bcf-8e7ba04593eb
cpe-central-worker-1 a3634fe4-e3c5-486d-918e-97df55ad476c
cpe-central-worker-2 c9410041-4b6e-4e17-8b8f-b7ffbf9525bc
cpe-central-worker-3 4c0fbb6a-ff80-4c5e-b783-46abccb04677
```

All UUIDs match their corresponding Nova instance IDs.

## Current Workarounds

- Ensure K8s node hostnames exactly match OpenStack instance names (fragile, not always possible)
- Set `--provider-id=openstack:///UUID` on kubelet at boot time (requires infra-level changes per node)

Both workarounds require manual coordination between infra provisioning and K8s node registration, which the UUID-based discovery would eliminate entirely.

## Additional Context

The silent failure when name matching fails (no error logged, providerID simply never set) makes debugging this issue very difficult. Even with `--v=2`, there is no indication that instance discovery failed. At minimum, a warning log when `getServerByName` returns no results would help operators diagnose mismatches.

Start in pkg/openstack/instances.go at getInstance() and getServerByName(), then trace the existing providerID discovery path. Implement systemUUID lookup before name matching, preserve the name fallback, and verify that successful discovery restores providerID and zone/region labels while failed lookups provide useful diagnostics.

Written by the indexing model from the issue text.