Referrals and product help in chat

New

• Referral rewards -- on the billing page when the program is enabled for your account: share link, email invites, unlockable reward slots, and referral activity.
• Product help in context chat -- ask what Unabyss is, how plans and trials work, or what your current limits are; replies link to the right in-app pages.

Improved

• MCP setup guides -- in-app guides tell agents to save context more liberally and add a Skills section (list_skills / get_skill).
• Context chat links -- in-app links in replies open in the same tab; external links still open in a new tab.

Fixed

• Social import progress -- imports stay "in progress" until memories are actually ready, and indexing failures surface clearly.
• Referral invitation page -- /ref/<code> shows a "just a moment" retry screen when the service is rate-limited instead of a generic dead end.