feat(legal): imprint & privacy notices, "Über MindSift"

- LEGAL_IMPRINT_/LEGAL_PRIVACY_ URL and Markdown (inline or *_FILE);
  only http(s) URLs accepted
- /auth/status exposes legal info; public GET /legal/{imprint|privacy}
- Links on login/setup screen and in the settings footer: URL opens a new
  tab, Markdown a reading modal; hidden when nothing is configured
- "Über MindSift" modal (version, license, repository) in settings and help
- Docs and compose/env examples

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/components/LegalLinks.tsx

@@ -0,0 +1,63 @@
+import React, { useState } from 'react';
+import { AuthStatus } from '../lib/types';
+import { api } from '../lib/api';
+import { MarkdownViewer } from '../lib/markdown';
+import { ReadingModal } from './ReadingModal';
+
+type LegalType = 'imprint' | 'privacy';
+const TITLES: Record<LegalType, string> = { imprint: 'Impressum', privacy: 'Datenschutz' };
+
+interface LegalLinksProps {
+  legal?: AuthStatus['legal'];
+  className?: string;
+  children?: React.ReactNode; // further footer links, e.g. "Über MindSift"
+}
+
+// Impressum / Datenschutz links: an external URL opens in a new tab, Markdown in a reading modal.
+// Links without URL or text are not shown at all.
+export const LegalLinks: React.FC<LegalLinksProps> = ({ legal, className = '', children }) => {
+  const [open, setOpen] = useState<{ type: LegalType; content: string } | null>(null);
+  const [error, setError] = useState<string | null>(null);
+
+  const entries = (['imprint', 'privacy'] as LegalType[])
+    .map((type) => ({
+      type,
+      url: type === 'imprint' ? legal?.imprintUrl : legal?.privacyUrl,
+      hasContent: type === 'imprint' ? legal?.hasImprintContent : legal?.hasPrivacyContent,
+    }))
+    .filter((e) => e.url || e.hasContent);
+
+  if (entries.length === 0 && !children) return null;
+
+  const openText = async (type: LegalType) => {
+    setError(null);
+    try {
+      setOpen({ type, content: await api.getLegalText(type) });
+    } catch (err: any) {
+      setError(err.message || 'Text konnte nicht geladen werden');
+    }
+  };
+
+  return (
+    <div className={`flex flex-wrap items-center justify-center gap-x-4 gap-y-1 text-[11px] text-muted ${className}`}>
+      {entries.map((e) =>
+        e.url ? (
+          <a key={e.type} href={e.url} target="_blank" rel="noopener noreferrer" className="hover:text-main underline-offset-2 hover:underline">
+            {TITLES[e.type]}
+          </a>
+        ) : (
+          <button key={e.type} type="button" onClick={() => openText(e.type)} className="hover:text-main underline-offset-2 hover:underline">
+            {TITLES[e.type]}
+          </button>
+        )
+      )}
+      {children}
+      {error && <span className="text-status-err">{error}</span>}
+      {open && (
+        <ReadingModal title={TITLES[open.type]} onClose={() => setOpen(null)}>
+          <MarkdownViewer content={open.content} />
+        </ReadingModal>
+      )}
+    </div>
+  );
+};