feat: add vision policy handling for image attachments

[cwebster-99]

Adds warning on image attachments when editor preview features is disabled

[Copilot]

Pull request overview

Adds organization policy awareness to chat image attachment rendering so users get a warning (and no preview) when preview features are disabled by policy.

Changes:

• Inject IDefaultAccountService into image-related attachment widgets to read account policy data.
• Add a policy check (chat_preview_features_enabled === false) to drive warning state for image attachments.
• Update image attachment pill/hover behavior to show a policy-based warning.

Comments suppressed due to low confidence (2)

src/vs/workbench/contrib/chat/browser/attachments/chatAttachmentWidgets.ts:471

• The hover text shown when the policy disables previews says "Vision is disabled by your organization", but the underlying policy flag is chat_preview_features_enabled (editor preview features). Consider rewording this message to match what is actually blocked here (image previews in chat) and/or that it’s a policy-controlled restriction, to avoid confusing users.

	if (visionDisabledByPolicy) {
		element.classList.add('warning');
		hoverElement.textContent = localize('chat.visionDisabledByOrganization', "Vision is disabled by your organization");
		disposable.add(hoverService.setupDelayedHover(element, {
			content: hoverElement,
			style: HoverStyle.Pointer,
		}));

src/vs/workbench/contrib/chat/browser/attachments/chatAttachmentWidgets.ts:834

• NotebookCellOutputChatAttachmentWidget now requires IDefaultAccountService too, which has the same impact on test and standalone instantiation as ImageAttachmentWidget (the standard workbenchInstantiationService doesn’t provide this service today). Please ensure a stub is registered in test service collections (or make the dependency optional with a safe default) so widget creation can’t throw due to a missing service.

		@INotebookService private readonly notebookService: INotebookService,
		@IInstantiationService private readonly instantiationService: IInstantiationService,
		@IDefaultAccountService private readonly defaultAccountService: IDefaultAccountService,
	) {

[Copilot]

@cwebster-99 I've opened a new pull request, #292594, to work on those changes. Once the pull request is ready, I'll request review from you.