style(frontend): Prettier config + one-time repo-wide format pass

Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing
hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass
(`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a
feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest
all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.

frontend/src/components/legal/LegalLayout.tsx

@@ -70,11 +70,19 @@ export default function LegalLayout({
           <div className="space-y-5 text-sm leading-relaxed text-fg/90">{children}</div>
         </div>
         <footer className="mt-6 flex flex-wrap gap-x-4 gap-y-1 text-xs text-muted">
-          <a href="/" className="hover:text-fg transition">Home</a>
-          <a href="/privacy" className="hover:text-fg transition">Privacy Policy</a>
-          <a href="/terms" className="hover:text-fg transition">Terms of Service</a>
+          <a href="/" className="hover:text-fg transition">
+            Home
+          </a>
+          <a href="/privacy" className="hover:text-fg transition">
+            Privacy Policy
+          </a>
+          <a href="/terms" className="hover:text-fg transition">
+            Terms of Service
+          </a>
           {contact && (
-            <a href={`mailto:${contact}`} className="hover:text-fg transition">Contact</a>
+            <a href={`mailto:${contact}`} className="hover:text-fg transition">
+              Contact
+            </a>
           )}
         </footer>
       </div>