fix(broker): topic_create no longer rejects on creator-seal failure

A bad ed25519 pubkey on the creator member (legacy data) made
sealTopicKeyForMember throw, which propagated up through createTopic
and made the WS topic_create handler never send a topic_created
frame. CLI saw a 5s timeout and printed 'topic create failed'.

Wraps the seal call in try/catch — topic creation succeeds even if
no copy gets sealed for the creator. They'll see GET /v1/topics/:name/key
return 404 until they re-seal (or a holder does it for them via
the phase-3 background loop).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/broker/src/broker.ts

@@ -593,13 +593,23 @@ export async function createTopic(args: {
   if (!row) throw new Error("failed to create topic");
 
   // Seal a copy for the creator immediately. Other members get sealed
-  // copies as they join via joinTopic().
+  // copies as they join (re-seal flow). Wrap in try/catch so a seal
+  // failure (bad pubkey, transient DB error) doesn't roll back topic
+  // creation — the user can re-seal later.
   if (args.createdByMemberId) {
-    await sealTopicKeyForMember({
-      topicId: row.id,
-      memberId: args.createdByMemberId,
-      bundle: topicKeyBundle,
-    });
+    try {
+      await sealTopicKeyForMember({
+        topicId: row.id,
+        memberId: args.createdByMemberId,
+        bundle: topicKeyBundle,
+      });
+    } catch (err) {
+      // Topic exists but no key sealed for the creator. They'll get
+      // 404 on GET /key until another holder re-seals. Phase-3 flow
+      // handles this for any member, including the creator.
+      // Silent in-band — the topic create itself succeeded.
+      void err;
+    }
   }
 
   return {