fix: show validation error when label is empty in NodeModal

Silent return when label was empty made the Add button appear broken.
Native browser required tooltip doesn't render in Radix Dialog portals.
Now shows inline red error message and highlights the field.

frontend/src/components/modals/NodeModal.tsx

@@ -43,13 +43,18 @@ export function NodeModal({ open, onClose, onSubmit, initial, title = 'Add Node'
   const [form, setForm] = useState<Partial<NodeData>>({ ...DEFAULT_DATA, ...initial })
   const [iconSearch, setIconSearch] = useState('')
   const [iconPickerOpen, setIconPickerOpen] = useState(false)
+  const [labelError, setLabelError] = useState(false)
 
   const set = (key: keyof NodeData, value: unknown) =>
     setForm((f) => ({ ...f, [key]: value }))
 
   const handleSubmit = (e: React.FormEvent) => {
     e.preventDefault()
-    if (!form.label?.trim()) return
+    if (!form.label?.trim()) {
+      setLabelError(true)
+      return
+    }
+    setLabelError(false)
     onSubmit(form)
     onClose()
   }
@@ -167,11 +172,11 @@ export function NodeModal({ open, onClose, onSubmit, initial, title = 'Add Node'
               <Label className="text-xs text-muted-foreground">Label *</Label>
               <Input
                 value={form.label ?? ''}
-                onChange={(e) => set('label', e.target.value)}
+                onChange={(e) => { set('label', e.target.value); if (labelError) setLabelError(false) }}
                 placeholder="My Server"
-                className="bg-[#21262d] border-[#30363d] text-sm h-8"
-                required
+                className={`bg-[#21262d] text-sm h-8 ${labelError ? 'border-[#f85149] focus-visible:ring-[#f85149]' : 'border-[#30363d]'}`}
               />
+              {labelError && <p className="text-[11px] text-[#f85149]">Label is required</p>}
             </div>
 
             {/* Hostname */}