Pigtails delivery report: Add team invitations

Original request

Add team invitations so workspace owners can invite teammates by email.

Clarifying questions

• Should only workspace owners be able to invite teammates?
• Should invites expire?
• Should revoked invites be blocked even if the email link is still open?
• Should a new user be able to create an account from the invite link?

Approved scope

Build owner-only workspace invites with pending, accepted, revoked, and expired states. Include invite acceptance for new users, workspace settings UI updates, permission checks, tests, and documentation.

Delivery plan

• Add invitation data model and lifecycle states
• Add owner-only invite creation from workspace settings
• Add invite acceptance route
• Enforce revoked and expired invite handling
• Add permission checks for non-owner users
• Update workspace invite documentation

Acceptance criteria

• Owner can invite a user by email
• Invited user can accept
• New user can create an account and join
• Non-owner cannot invite
• Revoked invite cannot be used
• Expired invite cannot be used
• Workspace settings UI updated
• Docs updated

Tests

• Unit tests passed
• Integration tests passed
• Permission tests passed
• Email rendering requires staging verification

Files changed

• invitation model
• workspace settings UI
• invite acceptance route
• permission checks
• docs/workspace-invites.md

Risks

Email delivery is mocked locally. Recommend staging email test before merge.