Add Team Invites to a SaaS App

PROJECT CONTEXT:
A multi-user SaaS app needs team invitation functionality so existing team admins or owners can invite other users by email, assign a role, and let invitees join the correct team securely.

GOAL:
Implement a working team invite system with database persistence, permission checks, invitation acceptance, duplicate prevention, expiration handling, and a usable invite management UI.

REQUIREMENTS:
- Create a database model for team invitations with team ID, email, role, token, inviter ID, status, and expiration timestamp
- Allow only authorized users such as team owners or admins to create invites
- Generate unique secure invite tokens that are stored and validated server-side
- Support inviting users by email with a selected team role
- Provide a way to send or display an invite link that can be shared with the recipient
- Accept an invite through a tokenized URL and add the user to the correct team
- Prevent duplicate active invites for the same email and team where appropriate
- Block acceptance of expired, revoked, or already accepted invites
- Prevent adding a user who is already a team member through invite acceptance
- Include an invite management screen to list pending and past invites
- Allow revoking pending invites
- Show clear success and error states for invite creation and acceptance

CONSTRAINTS:
- Use the app's existing auth system and current team/user models instead of creating parallel auth logic
- Do not fake email sending if email infrastructure does not exist; provide a shareable invite link fallback
- Do not store insecure plain-text secrets as the only validation mechanism
- Keep permissions enforced on the server, not only hidden in the UI

DEFINITION OF DONE:
- An authorized team admin or owner can create an invite for an email and role from the app UI
- A pending invite is persisted in the database with valid metadata and a secure token or token hash
- The invite link opens a real acceptance flow that validates token status and expiration
- Accepting a valid invite adds the authenticated user to the correct team with the assigned role
- Expired, revoked, duplicate, and already-used invites are rejected with clear errors
- Pending invites are visible in a team management view and can be revoked
- Users already in the team cannot be re-added through the invite flow
- The feature works end-to-end with real backend logic, not just UI placeholders

COMMON FAILURES TO AVOID:
- Building only an invite modal UI without any database table, token validation, or acceptance logic
- Letting the frontend decide who can invite users without server-side authorization checks
- Creating invite links that look real but do not actually map to stored invite records
- Accepting the invite visually without creating a real membership row in the database
- Ignoring edge cases like duplicate invites, expired tokens, revoked invites, or existing team membership