Improve tool recovery and browser runtime defaults

[Kaguya-19]

Summary

• Improve bash/tool failure guidance for foreground timeouts and background work by pointing agents toward bounded foreground runs or task_create + task_wait.
• Add browser-use runtime defaults for action/navigation timeout and optional Chromium proxy env configuration.
• Harden execute_code read-only probing against missing input and stabilize the Weixin nonblocking login test under node --test.

Validation

• npm run build
• node --test --test-force-exit --test-timeout 60000 dist/tests/gateway/weixin-nonblocking-login.spec.js
• node --test --test-force-exit --test-timeout 60000 dist/tests/tool/bash-result-display.spec.js dist/tests/tool/error-recovery.spec.js dist/tests/agent/sub/SubAgentSession.spec.js dist/tests/tool/builtin/executeCode.spec.js
• npm test