test: Update test suite with improved structure

- Update test_helper/common.bash with Docker utilities
- Update unit tests for build, firewall, and security
- Update integration tests for configuration
- Add simple_test.bats for basic testing
- Fix test assertions and error handling

💘 Generated with Crush

Assisted-by: GLM-4.6 via Crush <crush@charm.land>

tests/simple_test.bats

@@ -0,0 +1,13 @@
+#!/usr/bin/env bats
+# Simple test to validate bats setup
+
+# Set BATS_LIB_PATH to point to our bats libraries
+export BATS_LIB_PATH="/usr/lib/bats-core"
+
+# Load bats libraries directly
+source /usr/lib/bats-core/bats-support/src/output.bash
+source /usr/lib/bats-core/bats-support/src/error.bash
+
+@test "bats is working" {
+    true
+}