fix: auto-fix code issues (cron)

- 修复PEP8格式问题（行长度超过120字符）
- 修复类型注解（添加__init__和_get_db返回类型）
- 删除__pycache__缓存文件
- 优化长SQL查询语句格式

backend/export_manager.py

@@ -121,14 +121,17 @@ class ExportManager:
 
         # 生成 SVG
         svg_parts = [
-            f'<svg xmlns="http://www.w3.org/2000/svg" width="{width}" height="{height}" viewBox="0 0 {width} {height}">',
+            f'<svg xmlns="http://www.w3.org/2000/svg" width="{width}" height="{height}" '
+            f'viewBox="0 0 {width} {height}">',
             "<defs>",
-            '  <marker id="arrowhead" markerWidth="10" markerHeight="7" refX="9" refY="3.5" orient="auto">',
+            '  <marker id="arrowhead" markerWidth="10" markerHeight="7" '
+            'refX="9" refY="3.5" orient="auto">',
             '    <polygon points="0 0, 10 3.5, 0 7" fill="#7f8c8d"/>',
             "  </marker>",
             "</defs>",
             f'<rect width="{width}" height="{height}" fill="#f8f9fa"/>',
-            f'<text x="{center_x}" y="30" text-anchor="middle" font-size="20" font-weight="bold" fill="#2c3e50">知识图谱 - {project_id}</text>',
+            f'<text x="{center_x}" y="30" text-anchor="middle" font-size="20" '
+            f'font-weight="bold" fill="#2c3e50">知识图谱 - {project_id}</text>',
         ]
 
         # 绘制关系连线
@@ -440,7 +443,9 @@ class ExportManager:
         story.append(Paragraph("InsightFlow 项目报告", title_style))
         story.append(Paragraph(f"项目名称: {project_name}", styles["Heading2"]))
         story.append(
-            Paragraph(f"生成时间: {datetime.now().strftime('%Y-%m-%d %H:%M')}", styles["Normal"])
+            f"生成时间: {datetime.now().strftime('%Y-%m-%d %H:%M')}",
+            styles["Normal"],
+        )
         )
         story.append(Spacer(1, 0.3 * inch))