Add RabbitMQ validation, test scaffolding, and config refactor

- Extract ipl() from main() with env-aware error handling (fatal in prod, warn in dev)
- Add amqp::validate() — TCP reachability check for RabbitMQ at IPL
- Refactor config::load() into load() + load_from() for testability
- Add lib.rs to expose public API to integration test harness
- Add test fixture scaffolding: tests/fixtures/beds_test.toml, tests/common/mod.rs
- Add unit tests for amqp::validate() error paths (closed port, bad address)

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

src/lib.rs

@@ -0,0 +1,18 @@
+//! # lib.rs — BEDS Public API
+//!
+//! Exposes BEDS modules for use by the integration test harness. All
+//! application logic lives in the individual modules; this file re-exports
+//! what tests need to reach.
+//!
+//! ## Calling Agents
+//! - `tests/common/mod.rs` and all files under `tests/` — via `rustybeds::`
+//!
+//! **Author:** mks
+//! **Version:** 1.0
+//!
+//! ## History
+//! * `2026-04-02` - mks - original coding
+
+pub mod amqp;
+pub mod config;
+pub mod logging;