[建议 / Feature] Add visual indicator when app has or has not focus #814

提交前确认 · Pre-submission checklist

• 我已搜索过现有 issue，确认这不是重复提议 / I searched existing issues and confirmed this isn't a duplicate.
• 我已阅读 CONTRIBUTING.md / I've read CONTRIBUTING.md.

问题类别 · Category

UI / 界面体验 · UI / UX

涉及的 Agent 框架 · Agent framework

不涉及框架 · Not framework-specific

使用场景 · Use case

In a multi-monitor configuration, there is nothing to indicate whether the ZCode app has focus or not.

There is no title bar, there is no border. There is no visual difference between app in focus, and not in focus. Maximized or not, makes no difference.

When switching between apps via mouse or ALT-Tab it is easy to lose track of whether ZCode has focus or not. It becomes easy to accidentally press ESC and cancel work in progress, while thinking another app has focus.

建议方案 · Proposal

Apply a 50% grey filter to the entire window to indicate the app does not have focus.

Any visual change should work in both dark mode and light mode. 50% grey would work in both cases.

预期价值 · Expected value

All apps should display some difference between focus and no focus.

你认为的优先级 · Your perceived priority

低 · Low

你使用的 ZCode 版本 / 环境 · ZCode version / environment

v3.14.3 / Linux Ubuntu

补充材料 · Additional context

No response