feat(fullstack init --next): flatten nuxt-base-template into projects/app/ post-clone

[pascal-klesse]

Summary

lt fullstack init --next clones lenneTech/nuxt-base-starter (or
#next) into projects/app/, but the cloned repo is a wrapper —
the root package.json is the npm scaffolder create-nuxt-base,
and the actual Nuxt app lives at projects/app/nuxt-base-template/.
The generated monorepo's pnpm-workspace.yaml and the README's
cd projects/app && pnpm install && pnpm dev therefore point at the
wrapper, not the app, so install resolves the wrong dependencies and
pnpm dev has nothing to run.

This PR makes setupNuxt flatten the wrapper layout after a
successful clone: the contents of nuxt-base-template/ (including
dotfiles like .env.example, .gitignore, .npmrc) replace the
cloned root, and the wrapper-only files (index.js, pnpm-lock.yaml,
the scaffolder package.json, etc.) disappear. After the flatten,
projects/app/ IS the Nuxt app — exactly what the README and
workspace already assume.

Friction log

LLM-test 2026-05-03 #3 entry 20:30 — cd projects/app && pnpm install && pnpm dev fails because the cloned root is the
create-nuxt-base scaffolder. Workaround the friction-author
used: cd projects/app/nuxt-base-template && pnpm install --ignore-workspace && pnpm dev.

Before / After

Before                                  After
projects/app/                           projects/app/
├── package.json  (create-nuxt-base)    ├── package.json  (nuxt-base-template)
├── index.js                            ├── nuxt.config.ts
├── pnpm-lock.yaml                      ├── app/app.vue
├── README.md                           ├── .env.example
└── nuxt-base-template/                 └── …
    ├── package.json  (the real app)
    ├── nuxt.config.ts
    ├── app/app.vue
    └── …

Backward compatibility

• Both branches affected, intentional. Both main and next of
  nuxt-base-starter ship the wrapper today, so the flatten benefits
  the legacy default-branch path too — not just --next. If a future
  branch drops the wrapper and ships the app at the root, the flatten
  becomes a no-op (no nuxt-base-template/ subdir = nothing to do).
• Link mode untouched. --frontend-link is a symlink to the
  user's local checkout; flattening would tear out the source tree.
  The flatten only runs when templateHelper.setup returns
  method === 'clone'.
• Defense-in-depth. The template is staged into a sibling tmp
  dir before dest is wiped. If staging fails (corrupt clone, future
  repo reshape, or nuxt-base-template exists as a stray file rather
  than a directory), the original layout stays untouched and the
  flatten returns { flattened: false, reason }. The pre-flatten
  layout is annoying but functional — better than wiping a user's
  clone over an unexpected layout.

Test plan

• New unit suite __tests__/fullstack-init-next-flatten.test.ts
  covers the happy path (flatten happens, dotfiles survive,
  wrapper-only files are removed), the no-op path (already-flat
  layouts), the defensive abort (stray file at the subdir name),
  and a source-introspection guard so a future refactor can't
  silently drop the call site.
• Full Jest suite green (npm test — 165 passed, 1 skipped).
• Lint clean (npm run lint).
• Manual smoke: lt fullstack init --next --name lt-flatten-test --noConfirm against the rebuilt CLI confirmed
  projects/app/package.json has name: nuxt-base-template,
  projects/app/nuxt-base-template/ is gone, dotfiles
  (.env.example, .gitignore, .npmrc, .nuxtrc) survived,
  and nuxt.config.ts + app/ are at the project root.

🤖 Generated with Claude Code