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>

src/lib.rs

@@ -16,3 +16,4 @@
 pub mod amqp;
 pub mod config;
 pub mod logging;
+pub mod mongo;