Add MSC4522 username colors, release notes dialog, and profile layout fixes.

Replace legacy profile style metadata with MSC4133 profile fields, add in-app update notes, tighten account profile name spacing, and wire desktop media save helpers through the client.

src/app/components/updates-dialog/UpdateMarkdownViewer.tsx

@@ -0,0 +1,35 @@
+import React from 'react';
+import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
+import { resolveUpdateAssetUrl } from '../../data/updateNotes';
+import * as css from './UpdatesDialog.css';
+
+type UpdateMarkdownViewerProps = {
+  markdown: string;
+};
+
+export function UpdateMarkdownViewer({ markdown }: UpdateMarkdownViewerProps) {
+  if (!markdown.trim()) {
+    return null;
+  }
+
+  return (
+    <div className={css.Markdown}>
+      <ReactMarkdown
+        remarkPlugins={[remarkGfm]}
+        components={{
+          a: ({ href, children }) => (
+            <a href={href} target="_blank" rel="noreferrer noopener">
+              {children}
+            </a>
+          ),
+          img: ({ src, alt }) => (
+            <img src={resolveUpdateAssetUrl(src) ?? src} alt={alt ?? ''} loading="lazy" />
+          ),
+        }}
+      >
+        {markdown}
+      </ReactMarkdown>
+    </div>
+  );
+}