feat(ui): About dialog, Release Notes, and new-version banner

About (in the account menu) shows frontend/backend/database versions + build.
Release Notes renders per-version highlights with a commit-SHA reference; a
dismissible banner appears once after the running build's version changes and
links into the notes. Adds a reusable Modal shell and the release-notes data
(detailed v0.1.0).

frontend/src/components/VersionBanner.tsx

@@ -0,0 +1,43 @@
+import { useState } from "react";
+import { Sparkles, X } from "lucide-react";
+import { FRONTEND_VERSION, SEEN_VERSION_KEY } from "../lib/version";
+
+// Eye-catching, dismissible bar shown once after the running build's version changes
+// (compares the baked frontend version to the last one the user acknowledged).
+export default function VersionBanner({ onOpen }: { onOpen: () => void }) {
+  const [dismissed, setDismissed] = useState(false);
+  const seen = localStorage.getItem(SEEN_VERSION_KEY);
+  // Don't nag in un-stamped dev builds, or once this version has been seen.
+  const show = FRONTEND_VERSION !== "dev" && seen !== FRONTEND_VERSION && !dismissed;
+  if (!show) return null;
+
+  function markSeen() {
+    localStorage.setItem(SEEN_VERSION_KEY, FRONTEND_VERSION);
+    setDismissed(true);
+  }
+
+  return (
+    <div className="shrink-0 flex items-center gap-2 px-4 py-2 text-sm bg-accent/15 border-b border-accent/30 text-fg">
+      <Sparkles className="w-4 h-4 text-accent shrink-0" />
+      <span className="min-w-0">
+        Updated to <span className="font-semibold">v{FRONTEND_VERSION}</span> — see what's changed.
+      </span>
+      <button
+        onClick={() => {
+          onOpen();
+          markSeen();
+        }}
+        className="ml-1 px-2.5 py-1 rounded-lg font-semibold bg-accent text-accent-fg hover:opacity-90 transition"
+      >
+        Release notes
+      </button>
+      <button
+        onClick={markSeen}
+        title="Dismiss"
+        className="ml-auto p-1 rounded-md text-muted hover:text-fg hover:bg-card transition"
+      >
+        <X className="w-4 h-4" />
+      </button>
+    </div>
+  );
+}