Fix/Resolve panic issues in proxy-related code (#560)

* fix(proxy): change default port from 5000 to 15721

Port 5000 conflicts with AirPlay Receiver on macOS 12+.
Also adds error handling for proxy toggle and i18n placeholder updates.

* fix(proxy): replace unwrap/expect with graceful error handling

- Handle HTTP client initialization failure with no_proxy fallback
- Fix potential panic on Unicode slicing in API key preview
- Add proper error handling for response body builder
- Handle edge case where SystemTime is before UNIX_EPOCH

* fix(proxy): handle UTF-8 char boundary when truncating request body log

Rust strings are UTF-8 encoded, slicing at a fixed byte index may cut
in the middle of a multi-byte character (e.g., Chinese, emoji), causing
a panic. Use is_char_boundary() to find the nearest safe cut point.

* fix(proxy): improve robustness and prevent panics

- Add reqwest socks feature to support SOCKS proxy environments
- Fix UTF-8 safety in masked_key/masked_access_token (use chars() instead of byte slicing)
- Fix UTF-8 boundary check in usage_script HTTP response truncation
- Add defensive checks for JSON operations in proxy service
- Remove verbose debug logs that could trigger panic-prone code paths

src-tauri/src/proxy/response_processor.rs

@@ -9,7 +9,7 @@ use super::{
     usage::parser::TokenUsage,
     ProxyError,
 };
-use axum::response::Response;
+use axum::response::{IntoResponse, Response};
 use bytes::Bytes;
 use futures::stream::{Stream, StreamExt};
 use rust_decimal::Decimal;
@@ -72,7 +72,13 @@ pub async fn handle_streaming(
         create_logged_passthrough_stream(stream, ctx.tag, Some(usage_collector), timeout_config);
 
     let body = axum::body::Body::from_stream(logged_stream);
-    builder.body(body).unwrap()
+    match builder.body(body) {
+        Ok(resp) => resp,
+        Err(e) => {
+            log::error!("[{}] 构建流式响应失败: {e}", ctx.tag);
+            ProxyError::Internal(format!("Failed to build streaming response: {e}")).into_response()
+        }
+    }
 }
 
 /// 处理非流式响应
@@ -155,7 +161,10 @@ pub async fn handle_non_streaming(
     }
 
     let body = axum::body::Body::from(body_bytes);
-    Ok(builder.body(body).unwrap())
+    builder.body(body).map_err(|e| {
+        log::error!("[{}] 构建响应失败: {e}", ctx.tag);
+        ProxyError::Internal(format!("Failed to build response: {e}"))
+    })
 }
 
 /// 通用响应处理入口