Add retry logic for guest agent filesystem info in efficient polling

Related to #630

When using the efficient polling path (cluster/resources endpoint), guest
agent calls to GetVMFSInfo were made without retry logic. This could cause
transient "Guest details unavailable" errors during initialization when the
guest agent wasn't immediately ready to respond.

The traditional polling path already used retryGuestAgentCall for filesystem
info queries, providing resilience against transient timeouts. This commit
applies the same retry logic to the efficient polling path for consistency.

Changes:
- Wrap GetVMFSInfo call in efficient polling with retryGuestAgentCall
- Use configured guestAgentFSInfoTimeout and guestAgentRetries settings
- Ensures consistent behavior between traditional and efficient polling paths

This should resolve the transient initialization issue reported in #630 where
guest details were unavailable until after a reinstall/restart.

internal/monitoring/monitor.go

@@ -6131,7 +6131,16 @@ func (m *Monitor) pollVMsAndContainersEfficient(ctx context.Context, instanceNam
 							Uint64("current_maxdisk", diskTotal).
 							Msg("Guest agent enabled, querying filesystem info for accurate disk usage")
 
-						fsInfo, err := client.GetVMFSInfo(ctx, res.Node, res.VMID)
+						// Use retry logic for guest agent calls to handle transient timeouts (refs #630)
+						fsInfoRaw, err := m.retryGuestAgentCall(ctx, m.guestAgentFSInfoTimeout, m.guestAgentRetries, func(ctx context.Context) (interface{}, error) {
+							return client.GetVMFSInfo(ctx, res.Node, res.VMID)
+						})
+						var fsInfo []proxmox.VMFileSystem
+						if err == nil {
+							if fs, ok := fsInfoRaw.([]proxmox.VMFileSystem); ok {
+								fsInfo = fs
+							}
+						}
 						if err != nil {
 							// Log more helpful error messages based on the error type
 							errMsg := err.Error()