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>

scripts/vitest-global-setup.mjs

@@ -0,0 +1,20 @@
+import { execSync } from 'node:child_process';
+
+// Tests TRUNCATE between cases, so they MUST NOT touch the dev database. Run them
+// against an isolated `iios_test` DB (created + migrated here, once, before the suite).
+const TEST_URL = 'postgresql://iios:iios@localhost:5434/iios_test?schema=public';
+
+export default function setup() {
+  try {
+    execSync(`docker exec iios-db psql -U iios -d postgres -c "CREATE DATABASE iios_test"`, { stdio: 'pipe' });
+  } catch (e) {
+    const msg = String(e.stderr ?? e.stdout ?? e);
+    if (!/already exists/i.test(msg)) {
+      console.warn(`[vitest] could not create iios_test (is the iios-db container up?): ${msg.slice(0, 160)}`);
+    }
+  }
+  execSync('pnpm --filter @insignia/iios-service exec prisma migrate deploy', {
+    stdio: 'inherit',
+    env: { ...process.env, DATABASE_URL: TEST_URL },
+  });
+}