feat(service): outbox relay + thread read endpoint + replay (P1.5, P1 complete)

OutboxRelay: FOR UPDATE SKIP LOCKED claim, in-process bus publish, PENDING->
PUBLISHED with 30s backoff + idempotent-consumer ledger. GET /v1/threads/:id/
messages (policy-scoped). Replay + read specs green; vitest fileParallelism off
(shared DB). End-to-end HTTP smoke verified: idempotent ingest, read-back, 400
on missing key. 19 tests pass.

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

vitest.config.ts

@@ -14,5 +14,8 @@ 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.
+    fileParallelism: false,
   },
 });