Add toggle for thinking content in chat accessible view

[Copilot]

Adds a way to include or exclude “thinking” content in the chat response accessible view so screen reader users can align with the sighted experience. The toggle is exposed as a command and persists per profile.

• Accessible view behavior: gate thinking content rendering on a persisted preference and refresh accessible view content when it changes.
• Command surface: add a Chat command to toggle thinking inclusion/exclusion.
• Help text + coverage: document the toggle in accessibility help and extend tests for default/disabled behavior.

const includeThinking = isThinkingContentIncludedInAccessibleView(storageService);
storageService.store(
	CHAT_ACCESSIBLE_VIEW_INCLUDE_THINKING_STORAGE_KEY,
	!includeThinking,
	StorageScope.PROFILE,
	StorageTarget.USER
);

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add a command/kb to toggle thinking content inclusion/exclusion in the chat response accessible view</issue_title>
<issue_description>After discussing with @jooyoungseo, @rperez030 and @accesswatch, we decided that providing a way to toggle thinking content is ideal and most aligned with the sighted user experience.
</issue_description>

Comments on the Issue (you are @copilot in this section)

@meganrogge We'll only toggle thinking and we're thinking this is a power feature, no KB needed

• Fixes Add a command/kb to toggle thinking content inclusion/exclusion in the chat response accessible view #290018

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