- Add admin handlers and services for users, posts, comments, groups, and dashboard
- Implement role permission management with ability to view and update permissions
- Add database seeding for roles and Casbin permission policies
- Upgrade Casbin from v2 to v3 with GORM adapter for persistent policy storage
- Add admin-specific repository methods with filtering and pagination
- Register new admin API routes under /api/v1/admin/*
- Simplify InviteMembers to always send invite card directly to invitee
- Modify RespondInvite to check group join type (anyone vs need approval) before adding member
- Update SetGroupAddRequest to properly handle invite flow with invitee agreement and admin approval stages
- Add case-insensitive search using LOWER() in user repository
- Add random offset (0-50) for first page of recommended posts
- Update dependencies: remove gorilla/websocket, promote gomail to direct dependency
