mesh-tools — the tool runtime and AMQP broker binding

The per-node process that makes a module's tools serve on the mesh:
- broker-amqp.ts: a concrete AMQP implementation of the sdk's Broker
  contract (request/reply over a reply queue + correlation id, publish/
  subscribe over a topic exchange). Kept here, not in the sdk, so a
  broker-client change never rebuilds a module (ADR 0044).
- runtime.ts: bind the broker, import the assigned modules' tool
  entrypoints (each registers as it loads), serveTools. The thin wrapper.
- main.ts: the entrypoint, configured by MESH_BROKER_URL + MESH_TOOL_MODULES.
- Dockerfile: the container a node runs it as.

Verified over a REAL broker: the test spins LavinMQ (the mesh's broker),
the runtime serves a registered tool, a separate connection invokes it by
name over AMQP and gets the result, and an unknown tool is refused over
the wire. So 'modules can serve' is now running-on-the-mesh, not just
proven in a mock.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

.gitignore

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