feat(skills): 技能管理 - 支持后台维护一级分类 (#694)

Co-authored-by: ddcat666 <26564566+ddcat666@users.noreply.github.com>

backend/internal/database/skill_curation_roots.go

@@ -0,0 +1,15 @@
+package database
+
+import (
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"infinite-canvas/backend/internal/model"
+)
+
+func migrateSkillCurationRoots(tx *gorm.DB) error {
+	if err := tx.AutoMigrate(&model.SkillCurationRoot{}, &model.SkillCurationRootAssignment{}); err != nil {
+		return err
+	}
+	roots := model.DefaultSkillCurationRoots()
+	return tx.Clauses(clause.OnConflict{DoNothing: true}).Create(&roots).Error
+}