fix: 修复 sql.js Uint8Array 与 fs.writeFile 的兼容性问题

sql.js export() 返回 Uint8Array，需用 Buffer.from() 转换后再写入文件
解决潜在的类型不匹配错误

ts/src/runtime/core/graph_memory/graph_database.ts

@@ -54,7 +54,8 @@ export class GraphDatabase {
         await fs.mkdir(dir, true);
       }
       const data = this.db.export();
-      await fs.writeFile(dbPath, data.buffer as ArrayBuffer, { encoding: 'binary' });
+      // sql.js returns Uint8Array, convert to Buffer for writeFile compatibility
+      await fs.writeFile(dbPath, Buffer.from(data), { encoding: 'binary' });
     } catch (error) {
       console.error(`[GraphDatabase] Save failed: ${error}`);
     }