fix: 多项修复

- main.py: 加 _CNJSONResponse 修复 datetime 序列化时区(+00:00→+08:00)
- schemas/__init__.py: 加 _fmt_dt 函数和 sync_to_platform 字段
- ai_service.py: 评论 max_tokens 从 300 提升到 500 避免截断
- scheduler.py: datetime.utcnow() 全部改为 datetime.now()（北京时间）
- docker-compose.yml: MySQL 容器加 TZ=Asia/Shanghai
- Interactions.vue: 文章标题链接从系统配置读取域名，格式为 {域名}/huihui-h5/#/news/share?id={id}&login=no

backend/app/main.py

@@ -6,6 +6,20 @@ from contextlib import asynccontextmanager
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse
+import re as _re
+
+# 修复 Pydantic v2 把 naive datetime 序列化为 +00:00 的问题
+# 数据库存的是北京时间，应标记为 +08:00
+from fastapi.responses import Response
+from fastapi.encoders import jsonable_encoder
+import json as _json
+
+class _CNJSONResponse(JSONResponse):
+    def render(self, content) -> bytes:
+        text = _json.dumps(content, ensure_ascii=False, allow_nan=False)
+        # 把 +00:00 替换为 +08:00
+        text = _re.sub(r'(\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2})\+00:00', r'\1+08:00', text)
+        return text.encode('utf-8')
 
 from app.core.config import settings
 from app.core.database import init_db
@@ -13,6 +27,17 @@ from app.core.logger import logger
 from app.api import router
 from app.services.scheduler import scheduler_service
 
+# 自定义 datetime 序列化：数据库存的是北京时间，输出时标记为 +08:00
+from fastapi.encoders import jsonable_encoder
+import json as _json
+
+class ChinaDatetimeEncoder(_json.JSONEncoder):
+    def default(self, obj):
+        if isinstance(obj, datetime.datetime):
+            # 标记为 +08:00 时区
+            return obj.strftime("%Y-%m-%dT%H:%M:%S+08:00")
+        return super().default(obj)
+
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
@@ -29,7 +54,21 @@ async def lifespan(app: FastAPI):
     logger.info("🛑 系统已关闭")
 
 
-app = FastAPI(
+import datetime as _dt
+
+import datetime as _dt
+
+class _DatetimeJSONResponse(JSONResponse):
+    def render(self, content) -> bytes:
+        import json
+        def _default(obj):
+            if isinstance(obj, _dt.datetime):
+                return obj.strftime("%Y-%m-%dT%H:%M:%S+08:00")
+            raise TypeError(repr(obj))
+        return json.dumps(content, ensure_ascii=False, default=_default).encode('utf-8')
+
+app = FastAPI(default_response_class=_CNJSONResponse,
+
     title="AI虚拟用户新闻互动系统",
     description="基于AI驱动的虚拟用户新闻互动自动化平台",
     version="1.0.0",