Add MongoDB reachability validation to IPL sequence

- Add rec_services config section to beds.toml and test fixture
- Add RecNodeConfig struct; export from config module
- Add mongo::validate() and validate_all() — TCP ping per configured REC node
- Wire mongo::validate_all() into ipl() with env-aware error handling
- Add mongodb crate dependency (sync feature)
- Add unit tests for mongo validate error paths (closed port, bad address)
- Update README status table and project structure

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

claude.md

@@ -32,6 +32,7 @@ rustybeds/
 │   │   ├── mod.rs            # load() + load_from() — layered TOML config
 │   │   └── structs.rs        # Typed config structs (serde Deserialize)
 │   ├── amqp.rs               # RabbitMQ transport — validate(), future channel/queue ops
+│   ├── mongo.rs              # MongoDB transport — validate_all(), future adapter ops
 │   ├── lib.rs                # Public API surface for integration test harness
 │   ├── logging.rs            # tracing + journald + console mirror init
 │   └── main.rs               # ipl() sequence + main()