Fix sitemap URL detection to require .xml extension (#611)

Resolves issue where URLs containing 'sitemap' in path (like
https://nx.dev/see-also/sitemap) were incorrectly treated as XML
sitemaps, causing XML parsing errors.

- Changed detection to require both .xml extension AND 'sitemap' in path
- Fixes XML parsing error: "not well-formed (invalid token)"
- Maintains compatibility with existing test cases
- Now correctly identifies only actual XML sitemap files

Fixes #607

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

python/src/server/services/crawling/helpers/url_handler.py

@@ -29,7 +29,10 @@ class URLHandler:
             True if URL is a sitemap, False otherwise
         """
         try:
-            return url.endswith("sitemap.xml") or "sitemap" in urlparse(url).path
+            parsed = urlparse(url)
+            path = parsed.path.lower()
+            # Only match URLs that end with .xml and contain sitemap in the filename
+            return path.endswith(".xml") and "sitemap" in path
         except Exception as e:
             logger.warning(f"Error checking if URL is sitemap: {e}")
             return False