chore(deps): update node.js to v20.20.0 for security patch (#253)

This update addresses multiple security vulnerabilities:
- CVE-2025-55131: Buffer.alloc non-zerofilled (High)
- CVE-2025-55130: File system permissions bypass via symlinks (High)
- CVE-2025-59465: HTTP/2 server crash with malformed HEADERS (High)
- CVE-2025-59466: Uncatchable stack overflow error (Medium)
- CVE-2025-55132: fs.futimes() permission model bypass (Low)

Closes #249

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: kentaro-m

.node-version

@@ -1 +1 @@
-20.19.6
+20.20.0