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/fixtures/beds_test.toml

@@ -0,0 +1,51 @@
+# =============================================================================
+# BEDS Test Fixture — beds_test.toml
+# =============================================================================
+#
+# Canonical configuration fixture for all BEDS unit and integration tests.
+# Values here are test-safe: localhost services, known ports, no real creds.
+#
+# Load via tests/common/mod.rs::load_test_config() — do not call
+# config::load() directly from tests, as that reads the live config/beds.toml.
+#
+# AUTHOR:   mks
+# VERSION:  1.0
+#
+# HISTORY:
+# ========
+# 2026-04-02    mks     original coding
+# =============================================================================
+
+debug                 = true
+syslog                = false
+syslog_mirror_console = true
+audit_on              = false
+journal_on            = false
+
+[id]
+env_name = "dev"
+version  = "1.0"
+wbid     = "ms"
+
+[broker_services]
+queue_tag        = "test_"
+vhost            = "test"
+timer_violation  = 3000
+records_per_xfer = 5000
+keepalive        = true
+heartbeat        = 60
+use_ssl          = false
+cert_path        = "/etc/rabbitmq"
+
+[broker_services.app_server]
+host     = "127.0.0.1"
+port     = 5672
+api_port = 15672
+user     = "beds"
+pass     = "changeme"
+rpi      = 50
+
+[broker_services.app_server.instances]
+r_broker = 2
+w_broker = 2
+m_broker = 0