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/backend/api/system.py

@@ -1,5 +1,6 @@
 # 宇之然内容创作平台 - 系统管理API
 
+from sqlalchemy import func
 from datetime import datetime, date
 from fastapi import APIRouter, Depends
 from sqlalchemy.orm import Session

platform/backend/main.py

@@ -9,7 +9,7 @@ from fastapi.middleware.cors import CORSMiddleware
 from contextlib import asynccontextmanager
 import uvicorn
 
-from database import init_db
+from app.database import init_db
 from core.security import SECRET_KEY
 from api import auth, topics, system, publishing, articles, logs, admin
 

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"
+}