Fix storage/disk/backup disappearing for clusters with VerifySSL enabled

Related to #670, #657

The fix in v4.26.5 (commit 59a97f2e3) attempted to resolve storage disappearing
by preferring hostnames over IPs when TLS hostname verification is required
(VerifySSL=true and no fingerprint). However, that fix was ineffective because
the cluster discovery code was populating BOTH the Host and IP fields with the
IP address.

**Root Cause:**
In internal/api/config_handlers.go, the detectPVECluster function was setting:
- endpoint.Host = schemePrefix + clusterNode.IP (when IP was available)
- endpoint.IP = clusterNode.IP

This meant both fields contained the same IP address. When the monitoring code
tried to prefer endpoint.Host for TLS validation (internal/monitoring/monitor.go:
361-368), it was still getting an IP, causing certificate validation to fail
with "certificate is valid for pve01.example.com, not 10.0.0.44".

**Solution:**
Separate the Host and IP fields properly during cluster discovery:
- endpoint.Host = hostname (e.g., "https://pve01:8006") for TLS validation
- endpoint.IP = IP address (e.g., "10.0.0.44") for DNS-free connections

The existing logic in clusterEndpointEffectiveURL() can now correctly choose
between them based on TLS requirements.

**Impact:**
Users with VerifySSL=true who upgraded to v4.26.1-v4.26.5 and lost storage
visibility should now see storage, VM disks, and backups again after this fix.

internal/api/config_handlers.go

@@ -666,22 +666,22 @@ func detectPVECluster(clientConfig proxmox.ClientConfig, nodeName string, existi
 			}
 
 			// Build the host URL with proper port
-			// Prefer IP if available, otherwise use node name
-			nodeHost := clusterNode.IP
-			if nodeHost == "" {
-				nodeHost = clusterNode.Name
-			}
-			nodeHost = ensureHostHasPort(nodeHost, defaultPort)
-
+			// Store hostname in Host field (for TLS validation), IP separately
 			endpoint := config.ClusterEndpoint{
 				NodeID:   clusterNode.ID,
 				NodeName: clusterNode.Name,
-				Host:     schemePrefix + nodeHost,
 				GuestURL: findExistingGuestURL(clusterNode.Name, existingEndpoints),
 				Online:   clusterNode.Online == 1,
 				LastSeen: time.Now(),
 			}
 
+			// Populate Host field with hostname (if available) for TLS certificate validation
+			if clusterNode.Name != "" {
+				nodeHost := ensureHostHasPort(clusterNode.Name, defaultPort)
+				endpoint.Host = schemePrefix + nodeHost
+			}
+
+			// Populate IP field separately for DNS-free connections
 			if clusterNode.IP != "" {
 				endpoint.IP = clusterNode.IP
 			}
@@ -696,24 +696,25 @@ func detectPVECluster(clientConfig proxmox.ClientConfig, nodeName string, existi
 				Msg("All detected cluster nodes failed validation; falling back to cluster metadata")
 
 			for _, clusterNode := range unvalidatedNodes {
-				nodeHost := clusterNode.IP
-				if nodeHost == "" {
-					nodeHost = clusterNode.Name
-				}
-				if nodeHost == "" {
+				if clusterNode.Name == "" && clusterNode.IP == "" {
 					continue
 				}
-				nodeHost = ensureHostHasPort(nodeHost, defaultPort)
 
 				endpoint := config.ClusterEndpoint{
 					NodeID:   clusterNode.ID,
 					NodeName: clusterNode.Name,
-					Host:     schemePrefix + nodeHost,
 					GuestURL: findExistingGuestURL(clusterNode.Name, existingEndpoints),
 					Online:   clusterNode.Online == 1,
 					LastSeen: time.Now(),
 				}
 
+				// Populate Host field with hostname (if available) for TLS certificate validation
+				if clusterNode.Name != "" {
+					nodeHost := ensureHostHasPort(clusterNode.Name, defaultPort)
+					endpoint.Host = schemePrefix + nodeHost
+				}
+
+				// Populate IP field separately for DNS-free connections
 				if clusterNode.IP != "" {
 					endpoint.IP = clusterNode.IP
 				}