Summary: Complete MCP gateway host.docker.internal configuration

All changes complete:
- Updated gateway URL logic to support both localhost and host.docker.internal
- Added --add-host flag to AWF for all engines when MCP gateway enabled
- Comprehensive tests added and passing
- All builds and formats successful

Co-authored-by: pelikhan <[email protected]>

Author: Copilot

.github/workflows/issue-classifier.lock.yml

@@ -405,14 +405,14 @@ func getMCPGatewayURL(config *MCPGatewayConfig, forContainer bool) string {
 	if port == 0 {
 		port = DefaultMCPGatewayPort
 	}
-	
+
 	// When accessing from inside a container (AWF), use host.docker.internal
 	// When accessing from the host (health checks), use localhost
 	host := "localhost"
 	if forContainer {
 		host = "host.docker.internal"
 	}
-	
+
 	return fmt.Sprintf("http://%s:%d", host, port)
 }