feat: 目标添加级别字段，卡片显示级别和子目标数量，修复Modal重置

app/models.py

@@ -197,6 +197,7 @@ class Goal(db.Model):
     id = db.Column(db.Integer, primary_key=True)
     name = db.Column(db.String(100), nullable=False)
     content = db.Column(db.Text)
+    level = db.Column(db.String(20), default="入门")  # 启蒙/入门/进阶/熟练/精通
     created_at = db.Column(db.DateTime, default=datetime.now)
     updated_at = db.Column(db.DateTime, default=datetime.now, onupdate=datetime.now)
 
@@ -205,6 +206,7 @@ class Goal(db.Model):
             "id": self.id,
             "name": self.name,
             "content": self.content,
+            "level": self.level,
             "created_at": self.created_at.isoformat() if self.created_at else None,
             "updated_at": self.updated_at.isoformat() if self.updated_at else None,
         }