feat: add app-starter plugin (Next.js, Flutter, FastAPI bootstrap skills)

[aneebbaig]

Adds app-starter, a plugin that bootstraps new apps with current packages, no deprecated APIs, and a consistent house style.

Skills

• nextjs-app - Next.js App Router + TypeScript, Prisma/Postgres, next-auth, Tailwind with shadcn or Mantine. Private, open-source, or both.
• flutter-app - FVM-pinned SDK, clean architecture, Riverpod, an Either/Failure error model, Play Store release setup.
• fastapi-app - async SQLAlchemy 2.0, asyncpg, Alembic, Pydantic v2, JWT, Docker + Postgres.

What makes it useful

• Each skill checks the live registry (npm, pub.dev, PyPI) for current stable versions at scaffold time, so nothing is pinned from stale training data.
• Each skill takes a short project brief and asks its variant questions before generating anything.
• Shared rules cover production hardening, git and CI (auto-merge on green), and an open-source docs checklist.

Category: Development Engineering
Canonical repo: https://github.com/aneebbaig/app-starter-skills (MIT)