fix(proxy): resolve 404 error and auto-setup proxy targets

Issues fixed:
1. Route prefix mismatch - Live config was set to use /claude, /codex,
   /gemini prefixes but server only had routes without prefixes
2. Proxy targets not auto-configured - start_with_takeover only modified
   Live config but didn't set is_proxy_target=true for current providers

Changes:
- Add prefixed routes (/claude/v1/messages, /codex/v1/*, /gemini/v1beta/*)
  to server.rs for backward compatibility
- Remove URL prefixes from takeover_live_configs() - server can route
  by API endpoint path alone (/v1/messages=Claude, /v1/chat/completions=Codex)
- Add setup_proxy_targets() method that automatically sets current providers
  as proxy targets when starting proxy with takeover
- Unify proxy toggle in SettingsPage to use takeover mode (same as main UI)
- Fix error message extraction in useProxyStatus hooks
- Fix provider switch logic to check both takeover flag AND proxy running state

src-tauri/src/proxy/server.rs

@@ -148,17 +148,24 @@ impl ProxyServer {
             // 健康检查
             .route("/health", get(handlers::health_check))
             .route("/status", get(handlers::get_status))
-            // Claude API
+            // Claude API (支持带前缀和不带前缀两种格式)
             .route("/v1/messages", post(handlers::handle_messages))
-            // OpenAI Chat Completions API (Codex CLI)
+            .route("/claude/v1/messages", post(handlers::handle_messages))
+            // OpenAI Chat Completions API (Codex CLI，支持带前缀和不带前缀)
             .route(
                 "/v1/chat/completions",
                 post(handlers::handle_chat_completions),
             )
-            // OpenAI Responses API (Codex CLI)
+            .route(
+                "/codex/v1/chat/completions",
+                post(handlers::handle_chat_completions),
+            )
+            // OpenAI Responses API (Codex CLI，支持带前缀和不带前缀)
             .route("/v1/responses", post(handlers::handle_responses))
-            // Gemini API
+            .route("/codex/v1/responses", post(handlers::handle_responses))
+            // Gemini API (支持带前缀和不带前缀)
             .route("/v1beta/*path", post(handlers::handle_gemini))
+            .route("/gemini/v1beta/*path", post(handlers::handle_gemini))
             .layer(cors)
             .with_state(self.state.clone())
     }