fix: 将平台业务ID统一改为String并自动建表

- 抖音、B站、快手、微博的帖子/视频/评论ID从BigInteger改为String，
  避免PostgreSQL下字符串写入BIGINT报错及未来ID溢出风险
- B站dynamic_id改为String，修复API返回id_str被强转int导致的精度丢失
- 知乎提取器对content_id/question_id显式str()转换
- main.py启动数据库保存模式时自动建表，无需手动--init_db
- 同步更新相关老化测试

store/douyin/_store_impl.py

@@ -97,7 +97,7 @@ class DouyinDbStoreImplement(AbstractStore):
         Args:
             content_item: content item dict
         """
-        aweme_id = int(content_item.get("aweme_id"))
+        aweme_id = content_item.get("aweme_id")
         async with get_session() as session:
             result = await session.execute(select(DouyinAweme).where(DouyinAweme.aweme_id == aweme_id))
             aweme_detail = result.scalar_one_or_none()
@@ -118,7 +118,7 @@ class DouyinDbStoreImplement(AbstractStore):
         Args:
             comment_item: comment item dict
         """
-        comment_id = int(comment_item.get("comment_id"))
+        comment_id = comment_item.get("comment_id")
         async with get_session() as session:
             result = await session.execute(select(DouyinAwemeComment).where(DouyinAwemeComment.comment_id == comment_id))
             comment_detail = result.scalar_one_or_none()