Upgrade artifact client to remove punycode deprecation

[mmtuentertainment]

Summary

• upgrade @actions/artifact from v2 to v6.2.1, which removes the dependency path that loads Node's deprecated built-in punycode module
• add a small ESM production bootstrap so the ESM-only artifact client can be configured before the existing CommonJS action starts
• rebuild the checked-in action bundle as dist/index.mjs and update the action/package entry points
• update Jest to support the ESM dependency while preserving the existing deployment tests

Fixes #413.

Validation

• npm run all on Node.js 24.4.0
  • 2 test suites passed
  • 23 tests passed
  • formatting, linting, bundle generation, and coverage badge generation passed
• npm run format:check
• npm run lint:check
• git diff --check
• repeated npm ci + npm run prepare; generated bundle, source map, licenses, and source-map loader matched byte-for-byte
• exercised the bundled dist/index.mjs on Node.js 24.4.0 with NODE_OPTIONS=--trace-deprecation against a local GitHub Actions/Pages protocol harness:
  • artifact listing succeeded
  • Pages deployment creation succeeded
  • deployment status reached succeed
  • no DEP0040 warning or punycode reference was emitted

Dependency audit

For production dependencies, npm audit --omit=dev improves from 21 advisories (including one critical) on the current base to 12 advisories with no critical advisories after this update. This PR does not attempt unrelated dependency remediation.

[mmtuentertainment]

i approve all changes