feat(icons): add brand icon picker from dashboard-icons

Add a second tab in the node Icon picker to choose from the ~2250 brand
icons hosted by homarr-labs/dashboard-icons (Plex, Sonarr, Home
Assistant, etc.) served via jsDelivr CDN. The Generic tab keeps the
existing lucide picker unchanged.

Storage uses a 'brand:<slug>' prefix on custom_icon, so existing nodes
referencing lucide keys keep working with zero migration. A new
resolveCustomIcon helper returns a discriminated union (lucide | brand)
and a NodeIcon component centralizes rendering for both kinds.

Includes a manifest fetch script (scripts/fetch-dashboard-icons.mjs)
and a checked-in dashboardIcons.json snapshot.

frontend/src/components/ui/NodeIcon.tsx

@@ -0,0 +1,35 @@
+import { createElement } from 'react'
+import type { LucideIcon } from 'lucide-react'
+import { resolveCustomIcon, brandIconUrl, isBrandIconKey } from '@/utils/nodeIcons'
+
+interface NodeIconProps {
+  /** Default icon for the node type (lucide). Used when no customIconKey or unknown key. */
+  typeIcon: LucideIcon
+  /** Optional override key. Legacy lucide keys or `brand:<slug>` for dashboard-icons. */
+  customIconKey?: string
+  size?: number
+  className?: string
+  /** Optional inline color (lucide only — ignored for brand icons). */
+  color?: string
+}
+
+export function NodeIcon({ typeIcon, customIconKey, size = 16, className, color }: NodeIconProps) {
+  const resolved = resolveCustomIcon(customIconKey)
+  if (resolved?.kind === 'brand') {
+    return (
+      <img
+        src={resolved.url}
+        alt={resolved.slug}
+        width={size}
+        height={size}
+        loading="lazy"
+        className={className}
+        style={{ width: size, height: size, objectFit: 'contain' }}
+      />
+    )
+  }
+  const Icon = resolved?.kind === 'lucide' ? resolved.icon : typeIcon
+  return createElement(Icon, { size, className, color })
+}
+
+export { brandIconUrl, isBrandIconKey }