feat(ui): add desktop footer, legal custom link and about dialog

frontend/src/components/AppFooter.tsx

@@ -0,0 +1,45 @@
+import React from 'react';
+import { AuthStatus } from '../lib/types';
+import { APP_VERSION } from '../version';
+import { LegalLinks } from './LegalLinks';
+
+interface AppFooterProps {
+  legal?: AuthStatus['legal'];
+  onOpenAbout: () => void;
+}
+
+export const AppFooter: React.FC<AppFooterProps> = ({ legal, onOpenAbout }) => {
+  return (
+    <footer className="hidden sm:flex shrink-0 w-full max-w-6xl mx-auto px-4 py-2 items-center justify-between text-[11px] text-faint border-t border-border/40 select-none">
+      <div className="flex items-center gap-3">
+        <button
+          type="button"
+          onClick={onOpenAbout}
+          className="font-semibold text-muted hover:text-main transition-colors cursor-pointer"
+        >
+          MindSift
+        </button>
+        <button
+          type="button"
+          onClick={onOpenAbout}
+          className="font-mono hover:text-main transition-colors cursor-pointer"
+          title="Über MindSift & Versionsdetails"
+        >
+          {APP_VERSION}
+        </button>
+        <span className="text-border">·</span>
+        <button
+          type="button"
+          onClick={onOpenAbout}
+          className="hover:text-main transition-colors cursor-pointer underline-offset-2 hover:underline"
+        >
+          Über MindSift
+        </button>
+      </div>
+
+      <div className="flex items-center gap-3">
+        <LegalLinks legal={legal} className="!text-faint gap-3" />
+      </div>
+    </footer>
+  );
+};