fix: filter invalid kwargs from recommended next_url pagination

illust_recommended's next_url contains array params like "viewed[]"
which are invalid Python identifiers and crash **kwargs unpacking.
Filter to isidentifier() keys only so pagination works correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pixiv_client.py

@@ -26,7 +26,8 @@ class PixivClient:
 
     def _next_qs(self, next_url: str) -> dict:
         parsed = urlparse(next_url)
-        return {k: v[0] for k, v in parse_qs(parsed.query).items()}
+        # Filter out array-style keys like "viewed[]" — invalid as Python kwargs
+        return {k: v[0] for k, v in parse_qs(parsed.query).items() if k.isidentifier()}
 
     def get_login_url(self, code_challenge: str) -> str:
         return (