feat(broker): scaffold apps/broker workspace (bun WS runtime, no port yet)

- @claudemesh/broker package with bun dev/start scripts
- src/index.ts stub: WS server on BROKER_PORT, SIGTERM cleanup
- src/env.ts: Zod-validated env (BROKER_PORT, DATABASE_URL, STATUS_TTL_SECONDS, HOOK_FRESH_WINDOW_SECONDS)
- src/db.ts: re-exports Drizzle client from @turbostarter/db
- src/broker.ts + src/types.ts: placeholders for step 8 port
- README documents run commands, env vars, deploy targets
- tsconfig extends @turbostarter/tsconfig base
- eslint.config.js extends @turbostarter/eslint-config/base

Dependencies declared but not installed yet (ws, drizzle-orm, zod,
libsodium-wrappers + workspace deps). turbo.json unchanged: the global
dev task already has persistent=true + cache=false which is what the
broker needs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/broker/src/db.ts

@@ -0,0 +1,10 @@
+/**
+ * Postgres client re-export for the broker.
+ *
+ * The broker shares a Postgres instance with apps/web, accessed through
+ * the same Drizzle schema defined in @turbostarter/db. Importing the
+ * `db` binding from `@turbostarter/db/server` gives us a pre-wired
+ * client with the `mesh` pgSchema tables already in scope.
+ */
+export { db } from "@turbostarter/db/server";
+export { schema } from "@turbostarter/db/schema";