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>

Cargo.toml

@@ -9,4 +9,5 @@ config = "0.14"
 thiserror = "1"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"]}
-tracing-journald = "0.3"
+tracing-journald = "0.3"
+mongodb = { version = "3", features = ["sync"] }