Revert "feat: add task header highlight for visual status indication"

[hannesrudolph]

Reverts #11305 - It is not operating as intended as it does not always refresh when the window is not focused on and has false positive events.

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Important

Reverts task header highlight feature due to issues, removing related code, settings, and styles across multiple files.

• Behavior:
  • Reverts task header highlight feature due to refresh issues and false positives.
  • Removes taskHeaderHighlightEnabled from globalSettingsSchema in global-settings.ts.
• State Management:
  • Removes taskHeaderHighlightEnabled from ExtensionState in vscode-extension-host.ts.
  • Removes related logic in ClineProvider class in ClineProvider.ts.
• UI Components:
  • Removes highlight logic and CSS classes from TaskHeader.tsx.
  • Deletes related tests in TaskHeader.spec.tsx.
  • Removes settings and UI elements in SettingsView.tsx and UISettings.tsx.
• Localization:
  • Deletes task header highlight translations from various locale files.
• Styles:
  • Removes CSS for task header highlights in index.css.

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[roomote]

Rooviewer   See task

Clean revert with no issues found. All taskHeaderHighlightEnabled references are properly removed across types, provider, UI components, context, localization files, CSS, and tests. Existing tests (25/25) pass.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}