fix: auto-fix code issues (cron)

- 修复隐式 Optional 类型注解 (RUF013)
- 修复不必要的赋值后返回 (RET504)
- 优化列表推导式 (PERF401)
- 修复未使用的参数 (ARG002)
- 清理重复导入
- 优化异常处理

backend/export_manager.py

@@ -75,7 +75,10 @@ class ExportManager:
         self.db = db_manager
 
     def export_knowledge_graph_svg(
-        self, project_id: str, entities: list[ExportEntity], relations: list[ExportRelation],
+        self,
+        project_id: str,
+        entities: list[ExportEntity],
+        relations: list[ExportRelation],
     ) -> str:
         """
         导出知识图谱为 SVG 格式
@@ -220,7 +223,10 @@ class ExportManager:
         return "\n".join(svg_parts)
 
     def export_knowledge_graph_png(
-        self, project_id: str, entities: list[ExportEntity], relations: list[ExportRelation],
+        self,
+        project_id: str,
+        entities: list[ExportEntity],
+        relations: list[ExportRelation],
     ) -> bytes:
         """
         导出知识图谱为 PNG 格式
@@ -337,7 +343,9 @@ class ExportManager:
         return output.getvalue()
 
     def export_transcript_markdown(
-        self, transcript: ExportTranscript, entities_map: dict[str, ExportEntity],
+        self,
+        transcript: ExportTranscript,
+        entities_map: dict[str, ExportEntity],
     ) -> str:
         """
         导出转录文本为 Markdown 格式
@@ -417,7 +425,12 @@ class ExportManager:
 
         output = io.BytesIO()
         doc = SimpleDocTemplate(
-            output, pagesize=A4, rightMargin=72, leftMargin=72, topMargin=72, bottomMargin=18,
+            output,
+            pagesize=A4,
+            rightMargin=72,
+            leftMargin=72,
+            topMargin=72,
+            bottomMargin=18,
         )
 
         # 样式
@@ -510,7 +523,8 @@ class ExportManager:
                 )
 
             entity_table = Table(
-                entity_data, colWidths=[1.5 * inch, 1 * inch, 1 * inch, 2.5 * inch],
+                entity_data,
+                colWidths=[1.5 * inch, 1 * inch, 1 * inch, 2.5 * inch],
             )
             entity_table.setStyle(
                 TableStyle(
@@ -539,7 +553,8 @@ class ExportManager:
                 relation_data.append([r.source, r.relation_type, r.target, f"{r.confidence:.2f}"])
 
             relation_table = Table(
-                relation_data, colWidths=[2 * inch, 1.5 * inch, 2 * inch, 1 * inch],
+                relation_data,
+                colWidths=[2 * inch, 1.5 * inch, 2 * inch, 1 * inch],
             )
             relation_table.setStyle(
                 TableStyle(