chore: remove unused kimi-migration-legacy package

[liruifengv]

Related Issue

No related issue.

Problem

packages/kimi-migration-legacy is an empty placeholder: it only ever contained a package.json (no sources, dependencies, or scripts) and nothing in the repository imports it. The CLI uses the separate @moonshot-ai/migration-legacy package instead. Keeping the empty package around is confusing and leaves stale entries in flake.nix and the changeset config.

What changed

Remove the package directory and drop its entries from flake.nix (workspacePaths / workspaceNames) and the changeset config / README, then refresh the lockfile. The real @moonshot-ai/migration-legacy package is untouched.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works. (N/A — removing dead code)
• Ran gen-changesets skill, or this PR needs no changeset. (no changeset — internal-only cleanup)
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

⚠️ No Changeset found

Latest commit: ab24175

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[pkg-pr-new]

pnpm dlx https://pkg.pr.new/@moonshot-ai/kimi-code@ab24175

npx https://pkg.pr.new/@moonshot-ai/kimi-code@ab24175

commit: ab24175