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/ChannelAbout.tsx

@@ -6,7 +6,10 @@ import { linkify } from "../lib/linkify";
 // --- About-tab metadata helpers (shared by the channel page and the manager's About overlay) ---
 function displayName(code: string, lang: string, type: "region" | "language"): string {
   try {
-    return new Intl.DisplayNames([lang], { type }).of(type === "region" ? code.toUpperCase() : code) ?? code;
+    return (
+      new Intl.DisplayNames([lang], { type }).of(type === "region" ? code.toUpperCase() : code) ??
+      code
+    );
   } catch {
     return code;
   }
@@ -47,7 +50,9 @@ export default function ChannelAboutContent({ ch }: { ch: ChannelDetail }) {
   return (
     <>
       {ch.description ? (
-        <p className="text-sm whitespace-pre-wrap break-words leading-relaxed">{linkify(ch.description)}</p>
+        <p className="text-sm whitespace-pre-wrap break-words leading-relaxed">
+          {linkify(ch.description)}
+        </p>
       ) : (
         <p className="text-sm text-muted">{t("channel.noDescription")}</p>
       )}
@@ -75,7 +80,10 @@ export default function ChannelAboutContent({ ch }: { ch: ChannelDetail }) {
               <span className="inline-flex items-center gap-2">
                 {/^[A-Za-z]{2}$/.test(ch.country) && (
                   // Real SVG flag (flag-icons) — Windows/Chrome don't render flag emoji.
-                  <span className={`fi fi-${ch.country.toLowerCase()} rounded-sm shrink-0`} aria-hidden />
+                  <span
+                    className={`fi fi-${ch.country.toLowerCase()} rounded-sm shrink-0`}
+                    aria-hidden
+                  />
                 )}
                 {displayName(ch.country, i18n.language, "region")}
               </span>