Fix stale GitHub Packages references after npmjs migration

[kin0992]

What

Two leftover references to GitHub Packages from before the npmjs.org migration (#36):

• .npmrc — the @kin0992 scope still pointed at npm.pkg.github.com; now points to registry.npmjs.org (the public registry packages actually publish to).
• .changeset/README.md — the release-flow description still said "publishes to GitHub Packages"; updated to npmjs.org.

Why

Since #36, packages publish publicly to npmjs.org with provenance (release-reusable.yml authenticates against registry.npmjs.org, and CONSUMING.md documents anonymous pnpm add). Workspace installs were unaffected (workspace:*), but the stale scope override would route any real @kin0992 registry lookup to GitHub Packages (requiring a token), and the doc was misleading.

No package source changed, so no changeset.

🤖 Generated with Claude Code

[changeset-bot]

⚠️ No Changeset found

Latest commit: 752a42a

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