fix(release-notes): ring the newest entry when the highlight version is unknown

/code-review (S1, finding 3): C-3.19 switched the banner from CURRENT_VERSION (always
RELEASE_NOTES[0]) to FRONTEND_VERSION (VITE_APP_VERSION), which is "dev" in the Vite
dev server and can drift from the notes — so the modal highlighted nothing. The modal
(which already imports RELEASE_NOTES, keeping App decoupled) now falls back to the
newest note when the passed version isn't listed.

frontend/src/components/ReleaseNotes.tsx

@@ -20,13 +20,19 @@ export default function ReleaseNotes({
   highlight?: string;
 }) {
   const { t } = useTranslation();
+  // Ring the newest note if `highlight` isn't one of the listed versions — e.g. a Vite dev build
+  // where the caller's FRONTEND_VERSION is "dev", or a VERSION bump whose note hasn't landed yet —
+  // so the banner always rings *something* current instead of nothing.
+  const active = RELEASE_NOTES.some((r) => r.version === highlight)
+    ? highlight
+    : RELEASE_NOTES[0]?.version;
   return (
     <Modal title={t("about.releaseNotes")} onClose={onClose} maxWidth="max-w-2xl">
       <div className="flex flex-col gap-6">
         {RELEASE_NOTES.map((r) => (
           <section
             key={r.version}
-            className={highlight === r.version ? "rounded-xl ring-1 ring-accent/40 p-3 -m-3" : ""}
+            className={active === r.version ? "rounded-xl ring-1 ring-accent/40 p-3 -m-3" : ""}
           >
             <div className="flex items-baseline gap-2 flex-wrap">
               <h3 className="text-base font-semibold">v{r.version}</h3>