Support chat iframes are now properly labelled for screen readers

The embedded support chat iframes had no title attribute, which raised a frame-title violation in our accessibility audits and made the chat widget effectively invisible to screen reader users — they could tab to it but had no idea what they were tabbing into.

Each chat iframe now carries a descriptive title, so screen reader users hear something useful instead of "iframe" when focus lands on it. Audit reports come back clean on this rule across all three apps.