fix: 修复yichens_spider_v4.py两处bug

1. post_time加入ON CONFLICT UPDATE SET - 未来重爬时可更新post_time
2. author_username提取从user_link改为<b>标签 - 修复用户名抓不到的问题

crawlers/yichens_spider_v4.py

@@ -87,6 +87,7 @@ def save_post(post):
                 reply_count = EXCLUDED.reply_count,
                 view_count = EXCLUDED.view_count,
                 price = EXCLUDED.price,
+                post_time = EXCLUDED.post_time,
                 updated_at = CURRENT_TIMESTAMP
         """
         cur.execute(sql, (
@@ -462,10 +463,11 @@ def parse_userinfo_block(userinfo_div):
                 if dispuser_match:
                     user_id = dispuser_match.group(1)
         
-        # username
+        # username - from <b> tag inside userinfo div
         username = None
-        if user_link:
-            username = user_link.get_text(strip=True)
+        b_tag = userinfo_div.find('b')
+        if b_tag:
+            username = b_tag.get_text(strip=True)
         
         # transaction_level
         level_match = re.search(r'交易等级[：:]\s*([^\n]+)', text)