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>

tests/common/mod.rs

@@ -0,0 +1,39 @@
+//! # tests/common/mod.rs — Shared Test Helpers
+//!
+//! Provides shared fixtures and helper functions for all BEDS integration
+//! tests. Unit tests within source files use the same fixture path directly
+//! via `config::load_from()`.
+//!
+//! ## Usage
+//!
+//! In any integration test file under `tests/`:
+//! ```
+//! mod common;
+//! let cfg = common::load_test_config();
+//! ```
+//!
+//! **Author:** mks
+//! **Version:** 1.0
+//!
+//! ## History
+//! * `2026-04-02` - mks - original coding
+
+/// Path to the canonical test config fixture, relative to the workspace root.
+pub const TEST_CONFIG_PATH: &str = "tests/fixtures/beds_test.toml";
+
+/// Loads the canonical BEDS test configuration fixture.
+///
+/// Panics on failure — a missing or malformed test fixture is a broken test
+/// environment, not a recoverable error.
+///
+/// # Returns
+///
+/// A fully-deserialised `BedsConfig` from `tests/fixtures/beds_test.toml`.
+///
+/// # History
+///
+/// * `2026-04-02` - mks - original coding
+pub fn load_test_config() -> rustybeds::config::BedsConfig {
+    rustybeds::config::load_from(TEST_CONFIG_PATH, "")
+        .expect("test fixture beds_test.toml failed to load")
+}