Promote service modules to services/ directory; add AmqpConnection + async IPL

- Flat src/amqp.rs, src/mongo.rs, src/mariadb.rs promoted to src/services/{amqp,mongo,mariadb}/
- services/amqp/connection.rs: AmqpConnection struct with connect() and declare_exchange()
- services/amqp/error.rs: AmqpError type (thiserror, wraps lapin::Error)
- ipl() made async; #[tokio::main] added to main()
- IPL step 3b: authenticate to RabbitMQ + declare beds.events topic exchange (durable)
- Added lapin = "2" and tokio = { version = "1", features = ["full"] } to Cargo.toml
- 12 unit tests pass
- Docs: README, CLAUDE.md, wiki/04-ipl.md, wiki/06-queue-topology.md updated

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

src/services/amqp/mod.rs

@@ -0,0 +1,86 @@
+//! # services/amqp/mod.rs — AMQP Transport Module
+//!
+//! RabbitMQ transport layer. Provides IPL reachability validation and the
+//! `AmqpConnection` struct for authenticated broker sessions.
+//!
+//! ## Public Surface
+//! - `validate()` — TCP reachability check (IPL step 3)
+//! - `AmqpConnection` — authenticated connection + channel (IPL step 3b)
+//! - `EXCHANGE_NAME` — the canonical `beds.events` exchange name constant
+//!
+//! **Author:** mks
+//! **Version:** 1.0
+//!
+//! ## History
+//! * `2026-04-02` - mks - original coding (flat amqp.rs)
+//! * `2026-04-04` - mks - promoted to services/amqp/, added AmqpConnection struct
+
+pub mod connection;
+pub mod error;
+
+pub use connection::{AmqpConnection, EXCHANGE_NAME};
+pub use error::AmqpError; // will be used by broker pool error handling
+
+use std::net::TcpStream;
+use std::time::Duration;
+
+use crate::config::BrokerServicesConfig;
+
+/// Validates that the RabbitMQ broker is reachable via TCP.
+///
+/// Opens a TCP connection to the configured broker host and port. Does not
+/// authenticate or open an AMQP channel — reachability only. The connection
+/// is closed immediately after a successful connect.
+///
+/// Called at IPL step 3 as a fast pre-flight check before the more expensive
+/// `AmqpConnection::connect()` authentication step.
+///
+/// # Arguments
+///
+/// * `cfg` — broker services configuration block from `BedsConfig`
+///
+/// # Returns
+///
+/// `Ok(())` if the TCP handshake succeeds within 5 seconds.
+/// `Err(String)` with a descriptive message if the broker cannot be reached.
+///
+/// # History
+///
+/// * `2026-04-02` - mks - original coding
+pub fn validate(cfg: &BrokerServicesConfig) -> Result<(), String> {
+    let addr_str = format!("{}:{}", cfg.app_server.host, cfg.app_server.port);
+
+    let addr: std::net::SocketAddr = addr_str
+        .parse()
+        .map_err(|e| format!("Invalid broker address {}: {}", addr_str, e))?;
+
+    TcpStream::connect_timeout(&addr, Duration::from_secs(5))
+        .map_err(|e| format!("RabbitMQ unreachable at {}: {}", addr_str, e))?;
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::config::load_from;
+
+    fn test_cfg() -> crate::config::BedsConfig {
+        load_from("tests/fixtures/beds_test.toml", "")
+            .expect("test fixture beds_test.toml failed to load")
+    }
+
+    #[test]
+    fn validate_err_on_closed_port() {
+        let mut cfg = test_cfg();
+        cfg.broker_services.app_server.port = 1;
+        assert!(validate(&cfg.broker_services).is_err());
+    }
+
+    #[test]
+    fn validate_err_on_bad_address() {
+        let mut cfg = test_cfg();
+        cfg.broker_services.app_server.host = "not_a_valid_host!!!".to_string();
+        assert!(validate(&cfg.broker_services).is_err());
+    }
+}