feat: resolve live Nostr references in blog posts and add embeds

Support naddr/nevent/note slugs for unindexed posts, cache naddr lookups,
render Nostr embeds in markdown, and add a consistency check for events mirrors.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/lib/browserCache.ts

@@ -0,0 +1,52 @@
+// Lightweight TTL cache backed by localStorage so resolved Nostr data (author
+// profiles, long-form events) survives page reloads and navigation instead of
+// being re-queried from relays every visit. No-ops on the server and degrades
+// silently on quota/parse errors so it can never break rendering.
+
+const PREFIX = "bbe:nostr:";
+
+interface Entry<T> {
+  v: T;
+  t: number; // stored-at epoch ms
+}
+
+export function readCache<T>(key: string, ttlMs: number): T | null {
+  if (typeof window === "undefined") return null;
+  try {
+    const raw = window.localStorage.getItem(PREFIX + key);
+    if (!raw) return null;
+    const entry = JSON.parse(raw) as Entry<T>;
+    if (Date.now() - entry.t > ttlMs) {
+      window.localStorage.removeItem(PREFIX + key);
+      return null;
+    }
+    return entry.v;
+  } catch {
+    return null;
+  }
+}
+
+export function writeCache<T>(key: string, value: T): void {
+  if (typeof window === "undefined") return;
+  const payload = JSON.stringify({ v: value, t: Date.now() } satisfies Entry<T>);
+  try {
+    window.localStorage.setItem(PREFIX + key, payload);
+  } catch {
+    // Quota exceeded (or similar): evict our namespace and retry once.
+    try {
+      pruneNamespace();
+      window.localStorage.setItem(PREFIX + key, payload);
+    } catch {
+      // Give up silently — caching is best-effort.
+    }
+  }
+}
+
+// Removes every entry written by this cache to recover space when localStorage
+// is full. Only touches our own namespace.
+function pruneNamespace(): void {
+  for (let i = window.localStorage.length - 1; i >= 0; i--) {
+    const k = window.localStorage.key(i);
+    if (k && k.startsWith(PREFIX)) window.localStorage.removeItem(k);
+  }
+}