Add a brand kit domain model, repository, and dedicated page/route for
managing brand kits, plus a BrandKitSelector used on the home page and
canvas workspace. Home project creation and the workspace can attach a
brand kit to a project, with new i18n strings and a side-nav entry.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
