Decouple UserType, add Role entity and management

Removed all UserType logic and references, replacing them with a new Role model and management system. Introduced RoleManager service, repository, and API endpoint for role CRUD operations. Updated user flows and JWT claims to use RoleCode. Removed admin-only user CRUD endpoints. Updated DI, documentation, and error handling for consistency. Appsettings and DTOs now reflect the new role-based approach.

Utility/JwtTokenHelper.cs

@@ -22,20 +22,12 @@ public class JwtTokenHelper
 
     public async Task<string> GenerateToken(User user)
     {
-        // Load the user's usertype if not already loaded. (No role: authorization belongs to the ERP, which reads the
-        // person's role from its own tables - the token only says who the person is.)
-        if (user.UserType == null)
-        {
-            await _dbContext.Entry(user)
-                .Reference(u => u.UserType)
-                .LoadAsync();
-        }
-
         var claims = new List<Claim>
         {
             new Claim("UserId", user.Id.ToString()),
-            new Claim("UserTypeId", user.UserTypeId.ToString()),
-            new Claim("UserTypeCode", user.UserType?.Code ?? ""),
+            new Claim("RoleId", user.RoleCode ?? ""),
+            new Claim("RoleCode", user.RoleCode ?? ""),
+
             new Claim("NIC", user.Nic ?? ""),
             new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
             new Claim(JwtRegisteredClaimNames.Iat,