fix(a11y,client): improve focus handling and scrolling behavior in router

[brc-dd]

Before (key strokes are not shown, but I'm pressing tab after clicking):

Screen.Recording.2025-09-13.at.3.20.39.PM.mov

After:

Screen.Recording.2025-09-13.at.3.21.37.PM.mov

[brc-dd]

For skip link thing, it still needs #4940. But I'm thinking of going with <main id="main-content"> and link using #main-content instead of manually finding the first heading. I'll update that PR and add main element with id to home too.

[Copilot]

Pull Request Overview

This PR improves accessibility by centralizing focus handling in the router's scrollTo function, removing duplicate focus logic from individual components.

• Consolidated focus management logic into the router's scrollTo function
• Removed custom focus handling from VPSkipLink and VPDocOutlineItem components
• Added proper focus restoration for elements that are temporarily made focusable

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/client/theme-default/components/VPSkipLink.vue	Removed custom focus handling and simplified skip link implementation
src/client/theme-default/components/VPDocOutlineItem.vue	Removed custom onClick handler for focus management
src/client/app/router.ts	Enhanced scrollTo function with comprehensive focus handling and tabindex management

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