packages: convert wheels-i18n to 4.0 package format #2268

Follow-up from #2243 Phase 1.

wheels-dev/wheels-i18n is currently a Wheels 3.x plugin (has box.json with type: "cfwheels-plugins", classic index.cfm bootstrap, no package.json, no tests/).

To be registerable in the wheels-packages registry, it needs 4.0 conversion:

Scope

• Author package.json (name, version, wheelsVersion, provides.mixins)
• Port index.cfm lifecycle to the package CFC init() hook
• Add tests/ suite (use WheelsTest BDD)
• Update README to reflect 4.0 installation
• Tag v2.0.0 (major bump — 4.0 is breaking vs 3.x plugin format) and cut GH release
• Open PR on wheels-dev/wheels-packages adding packages/wheels-i18n/manifest.json

Acceptance

• Registry's validate.yml passes on the new manifest
• wheels packages install wheels-i18n works (once Phase 3 CLI ships)