fix(proxy): improve validation and error handling in proxy config panels

- Add StopTimeout/StopFailed error types for proper stop() error reporting
- Replace silent clamp with validation-and-block in config panels
- Add listenAddress format validation in ProxyPanel
- Use log_codes constants instead of hardcoded strings
- Use once_cell::Lazy for regex precompilation

src-tauri/src/services/skill.rs

@@ -160,7 +160,7 @@ impl SkillService {
                 .user_agent("cc-switch")
                 .timeout(std::time::Duration::from_secs(10))
                 .build()
-                .expect("Failed to create HTTP client"),
+                .unwrap_or_else(|_| Client::new()),
         }
     }