fix(support): agent-demo self-seeds (join default queue + go online); tickets always get a queue

Root cause of 'waiting for escalations': no queue/membership meant tickets were
never assigned. Now: createTicket find-or-creates a default queue; new joinDefault
endpoint + useGoOnline hook; agent-demo joins+goes-AVAILABLE on load (assignPending
picks up any waiting ticket). smoke-support self-seeds (no seed script needed).
Also: vitest singleFork to end cross-file DB races (45 tests deterministic).

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

vitest.config.ts

@@ -14,8 +14,12 @@ export default defineConfig({
   },
   test: {
     include: ['packages/**/src/**/*.{test,spec}.ts', 'test/**/*.{test,spec}.ts'],
-    // DB-backed specs share one Postgres and truncate tables between tests, so
-    // test files must not run in parallel against it.
+    // 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.
     fileParallelism: false,
+    sequence: { concurrent: false },
+    pool: 'forks',
+    poolOptions: { forks: { singleFork: true } },
   },
 });