fix: 修复 graph_nodes 表 weight 字段缺失问题

- 在 GraphNodes 模型中添加 weight 字段，设置默认值为 1.0
- 修复 Hippocampus.py 中插入 GraphNodes 时缺少 weight 字段的问题
- 解决 sqlite3.IntegrityError: NOT NULL constraint failed: graph_nodes.weight 错误

src/chat/memory_system/Hippocampus.py

@@ -928,6 +928,7 @@ class EntorhinalCortex:
                             "concept": concept,
                             "memory_items": memory_items_json,
                             "hash": memory_hash,
+                            "weight": 1.0,  # 默认权重为1.0
                             "created_time": created_time,
                             "last_modified": last_modified,
                         }
@@ -1084,6 +1085,7 @@ class EntorhinalCortex:
                                 "concept": concept,
                                 "memory_items": memory_items_json,
                                 "hash": self.hippocampus.calculate_node_hash(concept, memory_items),
+                                "weight": 1.0,  # 默认权重为1.0
                                 "created_time": data.get("created_time", current_time),
                                 "last_modified": data.get("last_modified", current_time),
                             }

src/common/database/sqlalchemy_models.py

@@ -361,6 +361,7 @@ class GraphNodes(Base):
     concept = Column(get_string_field(255), nullable=False, unique=True, index=True)
     memory_items = Column(Text, nullable=False)
     hash = Column(Text, nullable=False)
+    weight = Column(Float, nullable=False, default=1.0)
     created_time = Column(Float, nullable=False)
     last_modified = Column(Float, nullable=False)