fix: browser tool IPC timeout — add executeJsWithTimeout + isBrowserOpen guard

- browser.ts: add executeJsWithTimeout() wrapping executeJavaScript with 10-15s timeout
  (renderer 冻结时不再无限挂起导致 IPC 25s 超时)
- All browser functions (evaluate/extract/click/type/scroll/screenshot) check isBrowserOpen()
  before execution, return clear error instead of auto-recreating empty browser window
- tool-registry.ts: browser tool IPC timeout increased from 25s to 60s
- Root cause: heavy pages (718+ links) can freeze Chromium renderer, executeJavaScript hangs
  indefinitely; after browser_close, getAgentBrowser() auto-created blank window confusing agent

src/renderer/services/tool-registry.ts

@@ -806,11 +806,12 @@ export async function executeTool(toolName: string, args: Record<string, unknown
       };
     }
 
-    // 其他工具：IPC 调用 + 25 秒硬超时
+    // 其他工具：IPC 调用 + 硬超时（browser 工具 60 秒，其余 25 秒）
+    const timeoutMs = toolName.startsWith('browser_') ? 60000 : 25000;
     const result = await Promise.race([
       bridge.tool.execute(toolName, args),
       new Promise<ToolResult>((_, reject) =>
-        setTimeout(() => reject(new Error(`工具 ${toolName} IPC 超时（25秒）`)), 25000)
+        setTimeout(() => reject(new Error(`工具 ${toolName} IPC 超时（${Math.round(timeoutMs / 1000)}秒）`)), timeoutMs)
       )
     ]);
     logToolResult(toolName, result.success, result.success ? undefined : result.error);