fix: 数据库配置和缺失导入

- 切换到 SQLite（app/database.py）避免外部依赖
- system.py: 添加 func 导入
- main.py: 导入改为 app.database.init_db
- 前端 topics.html: Vue 应用结构修复
- 后端导入全面修正（绝对导入）

版本: v1.0.3 (完整可运行版)

platform/frontend/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "frontend",
+  "version": "1.0.0",
+  "description": "",
+  "main": "debug-vue.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "type": "commonjs"
+}