Docs: unify skeleton README

[ohmyfelix]

Scope

README-only onboarding audit on the existing PR branch. Uses create-project → make init → make setup → npm ci, requires the asset watcher initial build/manifest before make dev, and explicitly avoids claiming that the build watcher is a Vite development server.

Validation

• Clean temporary-copy Composer install, init/setup, and npm ci passed on PHP 8.5.3 / Composer 2.9.5 / Node 22.22.0 / npm 10.9.4.
• npm run watch completed its initial build and wrote www/dist/manifest.json; PHP HTTP smoke then passed.
• make qa passed.
• make tests passed (2 tests).
• README audit evaluator passed.
• git diff --check passed.
• PR diff contains only README.md.

Notes

npm ci reports 11 existing audit findings (4 moderate, 7 high); no dependencies were changed in this README-only PR.