Add npm links metadata

[yanziwei]

Summary

• add npm homepage metadata for sendbird-platform-sdk-typescript
• add npm bugs.url metadata pointing to the repository issue tracker

This is metadata-only. Runtime code, generated API files, dependencies, package version, exports, and build output are unchanged.

Validation

node metadata assertion for src/api/generated/package.json
git diff --check
(cd src/api/generated && npm pack --dry-run --ignore-scripts --json)

The dry-run package includes package.json.