feat: write snapshots to fixed filename snapshots.html

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

src/snapshot_downloader.py

@@ -599,7 +599,7 @@ class SnapshotDownloader:
         )
 
         # Generate filename
-        filename = f"snapshots_{date_from}_to_{date_to}.html"
+        filename = "snapshots.html"
         filepath = self.output_dir / filename
 
         # Generate HTML content