feat(web): favicon + toast feedback (polish)

Add a vinyl-record favicon (icon.svg) — fixes the favicon.ico 404 console
error. Lightweight toast system (ToastHost + toast()) fired on request, wanted
add, search, follow, and want actions so submits give explicit feedback.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/_ui/toast.tsx

@@ -0,0 +1,38 @@
+"use client";
+
+import { useEffect, useRef, useState } from "react";
+
+/** Fire a transient toast from anywhere: `toast("Queued")`. */
+export function toast(message: string) {
+  if (typeof window !== "undefined") {
+    window.dispatchEvent(new CustomEvent("lyra-toast", { detail: message }));
+  }
+}
+
+/** Renders toasts fired via `toast()`. Mounted once in the root layout. */
+export function ToastHost() {
+  const [items, setItems] = useState<{ id: number; text: string }[]>([]);
+  const nextId = useRef(0);
+
+  useEffect(() => {
+    function onToast(e: Event) {
+      const text = (e as CustomEvent<string>).detail;
+      const id = ++nextId.current;
+      setItems((xs) => [...xs, { id, text }]);
+      setTimeout(() => setItems((xs) => xs.filter((x) => x.id !== id)), 2600);
+    }
+    window.addEventListener("lyra-toast", onToast);
+    return () => window.removeEventListener("lyra-toast", onToast);
+  }, []);
+
+  if (items.length === 0) return null;
+  return (
+    <div className="toast-host" role="status" aria-live="polite">
+      {items.map((t) => (
+        <div key={t.id} className="toast">
+          {t.text}
+        </div>
+      ))}
+    </div>
+  );
+}