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>

vitest.config.ts

@@ -15,9 +15,13 @@ export default defineConfig({
   },
   test: {
     include: ['packages/**/src/**/*.{test,spec}.ts', 'test/**/*.{test,spec}.ts'],
-    // DB-backed specs share one Postgres and TRUNCATE between tests. Run every
-    // file in a single worker process, sequentially, so there is no cross-file
-    // race on the shared database.
+    // DB-backed specs TRUNCATE between tests, so they run against an ISOLATED
+    // `iios_test` database (created + migrated by the global setup) — never the dev
+    // DB. This env overrides any DATABASE_URL from the shell.
+    env: { DATABASE_URL: 'postgresql://iios:iios@localhost:5434/iios_test?schema=public' },
+    globalSetup: ['./scripts/vitest-global-setup.mjs'],
+    // Run every file in a single worker process, sequentially, so there is no
+    // cross-file race on the shared database.
     fileParallelism: false,
     sequence: { concurrent: false },
     pool: 'forks',