refactor: migrate signup functionality to single usersignup module

backend/internal/model/signup_token.go

@@ -1,29 +0,0 @@
-package model
-
-import (
-	"time"
-
-	datatype "github.com/pocket-id/pocket-id/backend/internal/model/types"
-)
-
-type SignupToken struct {
-	Base
-
-	Token      string            `json:"token"`
-	ExpiresAt  datatype.DateTime `json:"expiresAt" sortable:"true"`
-	UsageLimit int               `json:"usageLimit" sortable:"true"`
-	UsageCount int               `json:"usageCount" sortable:"true"`
-	UserGroups []UserGroup       `gorm:"many2many:signup_tokens_user_groups;"`
-}
-
-func (st *SignupToken) IsExpired() bool {
-	return time.Time(st.ExpiresAt).Before(time.Now())
-}
-
-func (st *SignupToken) IsUsageLimitReached() bool {
-	return st.UsageCount >= st.UsageLimit
-}
-
-func (st *SignupToken) IsValid() bool {
-	return !st.IsExpired() && !st.IsUsageLimitReached()
-}