fix(desktop): Added a Windows-only guard that makes window.getComputedStyle fall back to document.documentElement

[Eric-Guo]

What does this PR do?

Fix #9051 and #8666, tested in Windows by built a exe

My seeing error:

TypeError: Failed to execute 'getComputedStyle' on 'Window': parameter 1 is not of type 'Element'.
TypeError: parameter 1 is not of type 'Element'.
    at getComputedStyle$1 (http://tauri.localhost/assets/index-BMEaQ_KQ.js:1707:91066)
    at isOverflowElement (http://tauri.localhost/assets/index-BMEaQ_KQ.js:1707:89839)
    at getOverflowAncestors (http://tauri.localhost/assets/index-BMEaQ_KQ.js:1707:91733)
    at autoUpdate (http://tauri.localhost/assets/index-BMEaQ_KQ.js:1707:99252)
    at Object.fn (http://tauri.localhost/assets/index-BMEaQ_KQ.js:1707:105253)
    at runComputation (http://tauri.localhost/assets/index-BMEaQ_KQ.js:2:8250)
    at updateComputation (http://tauri.localhost/assets/index-BMEaQ_KQ.js:2:7981)
    at runTop (http://tauri.localhost/assets/index-BMEaQ_KQ.js:2:9466)
    at runUserEffects (http://tauri.localhost/assets/index-BMEaQ_KQ.js:2:10730)
    at http://tauri.localhost/assets/index-BMEaQ_KQ.js:2:10322

[github-actions]

Hey! Your PR title fix(app) Added a Windows-only guard that makes window.getComputedStyle fall back to document.documentElement doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[Copilot]

Pull request overview

This PR adds a Windows-specific workaround for a WebView2 issue where window.getComputedStyle can be called with non-Element values. The fix wraps the native getComputedStyle function to validate inputs and fall back to a safe element when needed.

Changes:

• Added Windows platform detection using navigator.platform
• Override window.getComputedStyle on Windows to handle invalid (non-Element) inputs from WebView2/Floating UI
• Fall back to document.documentElement when the input is not a valid Element

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