Unify integration test environment and add valid config validation

- Create shared tests/common.rs with TestEnvironment setup
- Simplify gemini_test_client.py to single-request client
- Refactor config validation tests to use common setup
- Add test_valid_config_startup for complete server validation
- Fix clippy warning in main.rs
- Remove unused code and consolidate test infrastructure

tests/common.rs

@@ -0,0 +1,59 @@
+use std::path::{Path, PathBuf};
+use tempfile::TempDir;
+
+pub struct TestEnvironment {
+    pub temp_dir: TempDir,
+    pub config_path: PathBuf,
+    pub cert_path: PathBuf,
+    pub key_path: PathBuf,
+    pub content_path: PathBuf,
+    pub port: u16,
+}
+
+pub fn setup_test_environment() -> TestEnvironment {
+    let temp_dir = TempDir::new().unwrap();
+    let config_path = temp_dir.path().join("config.toml");
+    let cert_path = temp_dir.path().join("cert.pem");
+    let key_path = temp_dir.path().join("key.pem");
+    let content_path = temp_dir.path().join("content");
+
+    // Create content directory and file
+    std::fs::create_dir(&content_path).unwrap();
+    std::fs::write(content_path.join("test.gmi"), "# Test Gemini content\n").unwrap();
+
+    // Generate test certificates
+    generate_test_certificates(temp_dir.path());
+
+    // Use a unique port based on process ID to avoid conflicts
+    let port = 1967 + (std::process::id() % 1000) as u16;
+
+    TestEnvironment {
+        temp_dir,
+        config_path,
+        cert_path,
+        key_path,
+        content_path,
+        port,
+    }
+}
+
+fn generate_test_certificates(temp_dir: &Path) {
+    use std::process::Command;
+
+    let cert_path = temp_dir.join("cert.pem");
+    let key_path = temp_dir.join("key.pem");
+
+    let status = Command::new("openssl")
+        .args(&[
+            "req", "-x509", "-newkey", "rsa:2048",
+            "-keyout", &key_path.to_string_lossy(),
+            "-out", &cert_path.to_string_lossy(),
+            "-days", "1",
+            "-nodes",
+            "-subj", "/CN=localhost"
+        ])
+        .status()
+        .unwrap();
+
+    assert!(status.success(), "Failed to generate test certificates");
+}