fix: redirect users based on role after login

- Admin users redirect to /admin dashboard
- Regular users redirect to home page /
- Prevents authorization errors for non-admin users

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

handlers/auth.go

@@ -55,7 +55,12 @@ func Login(db *gorm.DB) gin.HandlerFunc {
 			return
 		}
 
+		// Redirect based on user role: admins to /admin, others to home
+		if user.Role == models.RoleAdmin {
 			c.Redirect(http.StatusFound, "/admin")
+		} else {
+			c.Redirect(http.StatusFound, "/")
+		}
 	}
 }