feat: 更新 API 视图和序列化器

更新内容：
1. views.py
- 集成分块读取（所有文件操作强制使用 chunked=True）
- 集成语义摘要生成（SemanticSummaryGenerator）
- 记录变动行数（lines_changed）
- 记录数据源（source: local/database/manual）
- 完善 check_sync_status 支持 HARD_CONFLICT 状态
- get_file_diff 返回变动行数
- get_ignore_patterns 返回模式类型（glob/regex）

2. serializers.py
- 添加 status_display, source_display 字段
- 更新 LobsterMemorySerializer 包含 summary 字段
- 更新 SyncHistorySerializer 包含 lines_changed, source 字段

所有 API 接口已更新，支持完整功能。

backend/memory_app/serializers.py

@@ -5,6 +5,8 @@ from .models import LobsterMemory, SyncHistory
 class LobsterMemorySerializer(serializers.ModelSerializer):
     """龙虾记忆序列化器"""
 
+    status_display = serializers.CharField(source='get_status_display', read_only=True)
+
     class Meta:
         model = LobsterMemory
         fields = [
@@ -14,8 +16,10 @@ class LobsterMemorySerializer(serializers.ModelSerializer):
             'content',
             'hash',
             'status',
+            'status_display',
             'version',
             'size',
+            'summary',
             'created_at',
             'updated_at',
         ]
@@ -27,6 +31,7 @@ class SyncHistorySerializer(serializers.ModelSerializer):
 
     action_display = serializers.CharField(source='get_action_display', read_only=True)
     status_display = serializers.CharField(source='get_status_display', read_only=True)
+    source_display = serializers.CharField(source='get_source_display', read_only=True)
 
     class Meta:
         model = SyncHistory
@@ -38,11 +43,14 @@ class SyncHistorySerializer(serializers.ModelSerializer):
             'action_display',
             'status',
             'status_display',
+            'source',
+            'source_display',
             'old_version',
             'new_version',
             'old_hash',
             'new_hash',
             'file_size',
+            'lines_changed',
             'operator',
             'error_message',
             'execution_time',
@@ -56,9 +64,10 @@ class FileDiffSerializer(serializers.Serializer):
 
     file_path = serializers.CharField()
     lobster_id = serializers.CharField()
-    local_content = serializers.CharField(required=False)
-    db_content = serializers.CharField(required=False)
-    local_hash = serializers.CharField(required=False)
-    db_hash = serializers.CharField(required=False)
+    local_content = serializers.CharField(required=False, allow_null=True)
+    db_content = serializers.CharField(required=False, allow_null=True)
+    local_hash = serializers.CharField(required=False, allow_null=True)
+    db_hash = serializers.CharField(required=False, allow_null=True)
     status = serializers.CharField()
-    message = serializers.CharField(required=False)
+    message = serializers.CharField(required=False)
+    diff = serializers.DictField(required=False)