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

media_platform/zhihu/help.py

@@ -107,10 +107,10 @@ class ZhihuExtractor:
         Returns:
         """
         res = ZhihuContent()
-        res.content_id = answer.get("id")
+        res.content_id = str(answer.get("id") or "")
         res.content_type = answer.get("type")
         res.content_text = extract_text_from_html(answer.get("content", ""))
-        res.question_id = answer.get("question").get("id")
+        res.question_id = str(answer.get("question", {}).get("id") or "")
         res.content_url = f"{zhihu_constant.ZHIHU_URL}/question/{res.question_id}/answer/{res.content_id}"
         res.title = extract_text_from_html(answer.get("title", ""))
         res.desc = extract_text_from_html(answer.get("description", "") or answer.get("excerpt", ""))
@@ -135,7 +135,7 @@ class ZhihuExtractor:
 
         """
         res = ZhihuContent()
-        res.content_id = article.get("id")
+        res.content_id = str(article.get("id") or "")
         res.content_type = article.get("type")
         res.content_text = extract_text_from_html(article.get("content"))
         res.content_url = f"{zhihu_constant.ZHIHU_ZHUANLAN_URL}/p/{res.content_id}"
@@ -162,6 +162,8 @@ class ZhihuExtractor:
 
         """
         res = ZhihuContent()
+        res.content_id = str(zvideo.get("id") or "")
+        res.content_type = zvideo.get("type")
 
         if "video" in zvideo and isinstance(zvideo.get("video"), dict): # This indicates data from the creator's homepage video list API
             res.content_url = f"{zhihu_constant.ZHIHU_URL}/zvideo/{res.content_id}"
@@ -170,8 +172,6 @@ class ZhihuExtractor:
         else:
             res.content_url = zvideo.get("video_url")
             res.created_time = zvideo.get("created_at")
-        res.content_id = zvideo.get("id")
-        res.content_type = zvideo.get("type")
         res.title = extract_text_from_html(zvideo.get("title"))
         res.desc = extract_text_from_html(zvideo.get("description"))
         res.voteup_count = zvideo.get("voteup_count")