Replace GORM with bbolt for database operations

Migrated from GORM to bbolt for lightweight key-value storage, better aligning with project requirements. Updated repository methods to utilize bbolt's native APIs and removed dependencies associated with GORM.

setting/entity.go

@@ -1,7 +1,6 @@
 package setting
 
 type Setting struct {
-	ID    uint   `gorm:"primary_key"`
-	Code  string `gorm:"type:varchar(100);uniqueIndex;not null"`
-	Value string `gorm:"type:text"`
+	Code  string `json:"code"`
+	Value string `json:"value"`
 }