feat: add legal tabs and update header assets

Switch the legal page to tabbed EULA/privacy content with URL sync, update header styling, and migrate footer icons to Ant Design.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/components/markdown-renderer/index.tsx

@@ -0,0 +1,17 @@
+import React from "react"
+
+interface MarkdownRendererProps {
+  /** HTML string processed by vite-plugin-markdown */
+  html: string
+  /** Optional custom class name */
+  className?: string
+}
+
+export default function MarkdownRenderer({ html, className = "" }: MarkdownRendererProps) {
+  return (
+    <article
+      className={`prose prose-slate max-w-none dark:prose-invert ${className}`}
+      dangerouslySetInnerHTML={{ __html: html }}
+    />
+  )
+}