Implement Issue Question Answering Function and Ready for Production

[dcloud347]

This pull request introduces a user registration flow with invitation code support, new admin APIs for managing users and invitation codes, and several improvements to repository and issue handling. The main focus is on enhancing authentication, user management, and resource control.

User Registration and Authentication Enhancements:

• Added user registration endpoint requiring an invitation code, with validation and code consumption logic. [1] [2]
• Introduced the InvitationCode entity and service, supporting creation, validation, expiration, and usage tracking of invitation codes. [1] [2] [3] [4]

Admin APIs for User and Invitation Code Management:

• Added /user/list/ endpoint for admins to list all users, using the new UserResponse model. [1] [2]
• Added /invitation-code/create/ and /invitation-code/list/ endpoints for admins to create and view invitation codes.

Repository and Issue Handling Improvements:

• Improved repository upload logic to enforce per-user repository limits and check for repository existence per user when authentication is enabled.
• Modified issue answering logic to only deduct issue credits after successful processing, and improved service retrieval and validation flow. [1] [2] [3] [4] [5] [6]

Other Notable Changes:

• Added endpoint for users to set their GitHub token. [1] [2]
• Improved email validation and request models for user creation and login. [1] [2] [3]

API Router and Service Initialization Updates:

• Registered new routers for invitation code and user management in the main API router. [1] [2]
• Registered the InvitationCodeService in the service initialization logic. [1] [2] [3]