fix(ci): add xdg-utils for ARM64 AppImage and suppress dead_code warnings

- Add xdg-utils dependency for xdg-mime binary required by AppImage bundler
- Remove unused McpStatus struct from gemini_mcp.rs (duplicate of claude_mcp.rs)
- Add #![allow(dead_code)] to proxy models reserved for future type-safe API

src-tauri/src/proxy/providers/models/anthropic.rs

@@ -2,6 +2,8 @@
 //!
 //! 用于 Anthropic Messages API 的请求/响应格式转换
 
+#![allow(dead_code)]
+
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 

src-tauri/src/proxy/providers/models/openai.rs

@@ -2,6 +2,8 @@
 //!
 //! 用于 OpenAI Chat Completions API 的请求/响应格式转换
 
+#![allow(dead_code)]
+
 use serde::{Deserialize, Serialize};
 use serde_json::Value;