refactor: update data access layer to use GORM repositories

- Replace SQL-based queries with GORM repository calls
- Update all model interfaces to use repository pattern
- Fix compilation errors in core/model/ files
- Update mocks to match new repository interfaces
- Modify API handlers to use new repository layer
- Maintain backward compatibility with existing interfaces

🤖 Generated with [Claude Code](https://claude.ai/code)

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

core/model/user.go

@@ -37,7 +37,7 @@ func (model *Model) CreateUser(user *types.User) error {
 		return errors.New("email required")
 	}
 
-	re := regexp.MustCompile(".+@.+\\..+")
+	re := regexp.MustCompile(`.+@.+\..+`)
 
 	if re.FindString(user.Email) == "" {
 		return errors.New("invalid email address")
@@ -47,7 +47,7 @@ func (model *Model) CreateUser(user *types.User) error {
 		return errors.New("password required")
 	}
 
-	if user.AgreeToTerms != true {
+	if !user.AgreeToTerms {
 		return errors.New("must agree to terms")
 	}
 
@@ -123,7 +123,7 @@ func (model *Model) ResetPassword(email string) error {
 
 	if err != nil {
 		// Don't send back error so people can't try to find user accounts
-		log.Printf("Invalid email for reset password " + email)
+		log.Printf("Invalid email for reset password %s", email)
 		return nil
 	}
 
@@ -154,7 +154,7 @@ func (model *Model) ConfirmResetPassword(password string, code string) (*types.U
 	user, err := model.db.GetUserByResetCode(code)
 
 	if err != nil {
-		return nil, errors.New("Invalid code")
+		return nil, errors.New("invalid code")
 	}
 
 	passwordHash, err := model.bcrypt.GenerateFromPassword([]byte(password), model.bcrypt.GetDefaultCost())