Add npm support metadata

[yanziwei]

Summary

• add npm homepage metadata pointing to the Luma API documentation site
• add npm bugs metadata pointing to the repository issue tracker

Verification

• node manifest assertion
• git diff --check
• npm pack --dry-run --json --ignore-scripts

[cursor]

PR Summary

Low Risk
Manifest-only metadata with no runtime or API impact.

Overview
Adds standard npm package metadata so registry pages and tooling can link to the project correctly.

Sets homepage to https://lumalabs.ai and adds a bugs.url pointing at https://github.com/lumalabs/lumaai-node/issues. No library code, exports, or dependencies change.

^{Reviewed by Cursor Bugbot for commit 640fa94. Bugbot is set up for automated code reviews on this repo. Configure here.}