chore: bump @n24q02m/mcp-core to 1.21.0

[n24q02m-ci]

mcp-core released stable v1.21.0.

Changelog: https://github.com/n24q02m/mcp-core/releases/tag/v1.21.0

Action required

Bump the @n24q02m/mcp-core pin in this repo and regenerate lockfile:

• TypeScript: update @n24q02m/mcp-core in package.json → bun install
• Python: update n24q02m-mcp-core in pyproject.toml → uv lock

Then open a PR with title fix: bump mcp-core to 1.21.0.

Auto-created by mcp-core CD. See feedback_core_release_auto_issue.md.

[n24q02m]

Superseded by merged PR #1035, which updates @n24q02m/mcp-core to 1.22.0. Closing this older dependency tracking issue.