fix(iios): thread subject on create, graceful open_thread error, isolated test DB

- openThread/createThread accept a generic `subject` (group name) — stored on the
  thread, echoed via listThreads; kernel never interprets it.
- Gateway open_thread now returns an ACK'd { error } on failure instead of throwing
  (which never acked → clients hung on "loading"). Non-member/missing-thread opens
  fail cleanly.
- Tests run against an isolated `iios_test` database (vitest globalSetup creates +
  migrates it; test.env overrides DATABASE_URL) so `pnpm test` can never TRUNCATE the
  dev database again. Verified: full suite green, dev DB row counts unchanged.

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

packages/iios-service/src/messaging/message.gateway.ts

@@ -66,11 +66,20 @@ export class MessageGateway implements OnGatewayInit, OnGatewayConnection {
   }
 
   @SubscribeMessage('open_thread')
-  async openThread(@ConnectedSocket() client: Socket, @MessageBody() body: { threadId?: string; membership?: string; creatorRole?: string }) {
+  async openThread(@ConnectedSocket() client: Socket, @MessageBody() body: { threadId?: string; membership?: string; creatorRole?: string; subject?: string }) {
     const { principal } = client.data as SocketState;
-    const result = await this.messages.openThread(body?.threadId ?? null, principal, { membership: body?.membership, creatorRole: body?.creatorRole });
-    await client.join(result.threadId);
-    return result;
+    try {
+      const result = await this.messages.openThread(body?.threadId ?? null, principal, {
+        membership: body?.membership,
+        creatorRole: body?.creatorRole,
+        subject: body?.subject,
+      });
+      await client.join(result.threadId);
+      return result;
+    } catch (err) {
+      // Fail to an ACK'd error instead of throwing (which never acks → client hangs on "loading").
+      return { error: (err as Error).message ?? 'could not open the conversation' };
+    }
   }
 
   @SubscribeMessage('add_participant')