fix(proxy): harden error handling and input validation

- Handle RwLock poisoning in settings.rs with unwrap_or_else
- Add fallback for dirs::home_dir() in config modules
- Normalize localhost to 127.0.0.1 in ProxyPanel
- Format IPv6 addresses with brackets for valid URLs
- Strict port validation with pure digit regex
- Treat NaN as validation failure in config panels
- Log warning on cost_multiplier parse failure
- Align timeoutSeconds range to [0, 300] across all panels

src-tauri/src/proxy/response_processor.rs

@@ -372,7 +372,12 @@ async fn log_usage_internal(
         Ok(Some(p)) => {
             if let Some(meta) = p.meta {
                 if let Some(cm) = meta.cost_multiplier {
-                    Decimal::from_str(&cm).unwrap_or(Decimal::from(1))
+                    Decimal::from_str(&cm).unwrap_or_else(|e| {
+                        log::warn!(
+                            "cost_multiplier 解析失败 (provider_id={provider_id}): {cm} - {e}"
+                        );
+                        Decimal::from(1)
+                    })
                 } else {
                     Decimal::from(1)
                 }