Add a Working Team Invite System to a SaaS App

PROJECT CONTEXT:
You are adding a teammate invitation system to an existing SaaS app with user accounts and workspace or team membership. The feature must let an authorized user invite someone by email, send or generate an invite link, track invite status, and let the recipient accept the invite into the correct workspace.

GOAL:
Implement a complete, working invite system with backend logic, database support, UI, validation, and acceptance flow that actually updates membership records.

REQUIREMENTS:
- Only authorized users such as workspace owners or admins can send invites
- Invites must be tied to a specific workspace or team
- Each invite must store invitee email, inviter, role, status, token, and expiration
- Invite tokens must be unique, hard to guess, and validated on acceptance
- The app must support accepting an invite for a new or existing user account
- Accepting an invite must create or update the workspace membership record
- Expired, revoked, or already accepted invites must be blocked with clear messages
- The inviter must be able to view pending invites
- The inviter should be able to resend or revoke an invite
- The UI must include loading, success, and error states
- Duplicate active invites for the same email and workspace should be prevented or handled intentionally

CONSTRAINTS:
- Do not build a fake front-end-only flow; membership changes must persist in the database
- Do not assume email sending is already configured; support either real email integration or a visible fallback invite link for testing
- Keep the implementation compatible with the app's existing auth and workspace model
- Do not grant access until the invite is actually accepted
- Do not allow unauthorized users to invite members

DEFINITION OF DONE:
- An authorized user can submit an email invite for a workspace and a real invite record is created
- The system produces a valid invite link containing a secure token
- A recipient can open the invite, authenticate or sign up, and accept it
- Accepting the invite creates the correct workspace membership with the intended role
- The same invite cannot be accepted twice
- Expired or revoked invites are rejected with correct UI feedback
- Pending invites are visible in the workspace settings or members area
- A workspace admin or owner can revoke an invite and the revoked link stops working

COMMON FAILURES TO AVOID:
- Building only a modal or form without any backend invite persistence
- Creating invite links that are not validated server-side
- Marking invites as accepted in the UI without creating membership records
- Letting any logged-in user send invites regardless of role
- Forgetting expiration, duplicate invite handling, or revoke logic
- Accept flow works for existing users only and breaks for new signups