fix(desktop): Reveal scrollbar in settings dialog panels of desktop app (such that keyboard navigation and mice with out scroll functionality work)

[JaapHaitsma]

The settings dialog panels scrolled but hid their scrollbar entirely, so there was no indication content continued below the fold (e.g. the Appearance / Color scheme setting) and no thumb to drag. Route the General, Keybinds, Providers and Models panels — in both the current and new-layout dialogs — through the shared ScrollView so a thumb reveals on hover.

Also make ScrollView defer to a descendant that already handled a key (e.defaultPrevented) so it no longer scrolls the panel when a focused dropdown is opened with the arrow keys.

Issue for this PR

Closes #34108

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

It introduces the same thin scrollbar that appears on hover as in other windows and dialogs in the settings. There was no indication before and with keyboard you could not scroll in the settings dialog. Also a mouse without a scroll wheel could not interact with it

How did you verify your code works?

I ran the Desktop app

Screenshots / recordings

and in the new layout

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Hey! Your PR title Reveal scrollbar in settings dialog panels of desktop app (such that keyboard navigation and mice with out scroll functionality work) 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).

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[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍