Implement invitations

[michaeleii]

This pull request includes significant updates to both the SignIn component and the convex backend, focusing on improving user experience and enhancing security checks. The changes include adding error handling and loading states in the SignIn component, and implementing comprehensive user and organization validation in the backend mutations and queries.

Frontend Changes:

• Error Handling and Loading States in SignIn Component:
  • Added error state and loading indicators to provide better user feedback during sign-in attempts. (app/sign-in.tsx) [1] [2] [3] [4]

Backend Changes:

• Enhanced User and Organization Validation:
  • Added checks to ensure users are authenticated and belong to the correct organization before performing actions such as creating, updating, or deleting challenges. (convex/challenges.ts) [1] [2] [3] [4] [5] [6] [7] [8]
  • Improved invitation handling by adding user role checks and updating invitation statuses. (convex/invitations.tsx) [1] [2] [3]

Email Components:

• Updated Email Links and Styles:
  • Modified email components to include dynamic links and enhanced styles for better user experience. (convex/emails/LTUserInvitation.tsx, convex/emails/LTWelcome.tsx, convex/emails/LTLoginOTP.tsx) [1] [2] [3] [4] [5] [6]

These changes aim to improve the overall user experience and ensure better security and data integrity in the application.