Add admin-disabled vision tooltip for image attachments

[Copilot]

When an image is attached to chat but vision is unavailable, the reference is currently greyed out with a generic “model does not support images” warning. For biz/enterprise users with editor preview features disabled by policy, the hover text should instead indicate admin-disabled vision support.

• Attachment status messaging
  • Update image and file attachment reference rendering to emit a policy-specific tooltip when preview features are disabled for business/enterprise tokens.
• Coverage
  • Add a unit test to assert the admin-disabled tooltip in FileVariable rendering.

const copilotToken = this.authService.copilotToken;
if (copilotToken && !copilotToken.isEditorPreviewFeaturesEnabled()) {
	const plan = copilotToken.copilotPlan;
	if (plan === 'business' || plan === 'enterprise') {
		return l10n.t("Vision support is disabled by your admin.");
	}
}

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