fix(proxy): preserve URL query/fragment and improve error handling

Extract shared URL utilities to handle query strings and fragments correctly.
Add race condition fix for URL preview, improve proxy toggle error feedback,
and support Codex chat format proxy endpoint.

src-tauri/src/proxy/providers/gemini.rs

@@ -9,6 +9,7 @@
 use super::{AuthInfo, AuthStrategy, ProviderAdapter, ProviderType};
 use crate::provider::Provider;
 use crate::proxy::error::ProxyError;
+use crate::proxy::url_utils::split_url_suffix;
 use reqwest::RequestBuilder;
 
 /// Gemini 适配器
@@ -200,7 +201,8 @@ impl ProviderAdapter for GeminiAdapter {
     }
 
     fn build_url(&self, base_url: &str, endpoint: &str) -> String {
-        let base_trimmed = base_url.trim_end_matches('/');
+        let (base, suffix) = split_url_suffix(base_url);
+        let base_trimmed = base.trim_end_matches('/');
         let endpoint_trimmed = endpoint.trim_start_matches('/');
 
         let mut url = format!("{base_trimmed}/{endpoint_trimmed}");
@@ -214,7 +216,7 @@ impl ProviderAdapter for GeminiAdapter {
             }
         }
 
-        url
+        format!("{url}{suffix}")
     }
 
     fn add_auth_headers(&self, request: RequestBuilder, auth: &AuthInfo) -> RequestBuilder {