Add tests for config error reporting and multi-vhost startup

Test that the server correctly reports missing certificate errors,
rejects invalid hostnames, fails gracefully on port conflicts, and
starts successfully with multiple virtual hosts configured.

tests/rate_limiting.rs

@@ -35,6 +35,7 @@ key = "{}"
     let mut server_process = std::process::Command::new(env!("CARGO_BIN_EXE_pollux"))
         .arg("--config")
         .arg(&config_path)
+        .arg("--quiet")
         .arg("--test-processing-delay")
         .arg("3") // 3 second delay per request
         .spawn()