duncanmcqueen brings DingDuff case law into the chat

This fork makes DingDuff's case materials available inside an assistant conversation, while keeping the connection's sign-in path tightly controlled.

Instead of sending lawyers out to a separate research tab, the proposed connection lets the assistant work with DingDuff, a case-law service, during a chat.

Find relevant cases through DingDuff.
Read case material within the conversation.
Locate documents tied to a particular case.

The work also resolves a practical sign-in obstacle where DingDuff's authorisation information lives behind a redirect. Those redirects are checked at every step, with sensitive credentials removed when a request moves to another site. When DingDuff is available, the chat uses it as the single case-law source for that exchange rather than blending results with the built-in alternative.

The change is still proposed, but its tests cover the redirect safeguards and the reported backend checks are clean.