Create a `deckio-starter` template repo for one-click Dev Container / Codespaces onboarding

[DevSecNinja]

Summary

Create a dedicated deckio-starter template repository in the deckio-art organization so new users can spin up a working DECKIO presentation project in one click — via a local Dev Container or a GitHub Codespace — without manually scaffolding.

Motivation

Today the onboarding path for a new user is:

1. Run npm create deckio my-talk
2. cd my-talk && npm install
3. npm run dev
4. Drive the deck with GitHub Copilot in Agent mode

This works, but it assumes the user has a local Node toolchain and knows the CLI flow. A template repo (marked as a GitHub "template", so users click Use this template) would let someone go from zero to a live, hot-reloading deck with Copilot instructions/skills preloaded — entirely in the browser via Codespaces, or locally via the Dev Containers extension.

This mirrors the dev-container setup that already lives in this engine repo under .devcontainer/, but packaged for end users building their own decks rather than for engine contributors.

Proposed solution

A new repo deckio-art/deckio-starter containing:

• .devcontainer/
  • devcontainer.json — Node image, forwards Vite port 5173, opens a preview on auto-forward, installs the recommended VS Code extensions (GitHub Copilot + Copilot Chat at minimum).
  • postCreateCommand that scaffolds the deck (e.g. npx create-deckio .) and runs npm install.
• VS Code task Start DECKIO (the npm run dev task) so users can launch the dev server from the command palette.
• A short README explaining the two entry points:
  • Use this template → Create a codespace
  • Clone locally → Reopen in Container
• Preloaded Copilot instructions + skills (inherited from @deckio/deck-engine via the scaffold).
• Repo flagged as a template repository in settings.

Acceptance criteria

• deckio-art/deckio-starter exists and is marked as a template repository.
• Clicking Use this template → Create a codespace on main yields a running deck at the forwarded port with no manual steps.
• Reopen in Container works locally with the Dev Containers extension.
• GitHub Copilot (Chat + Agent mode) is available and the DECKIO skills/instructions are present in the scaffolded project.
• README documents both the Codespaces and local Dev Container flows.

Open questions

• Should the starter pin a specific @deckio/deck-engine version, or always scaffold the latest?
• Should we offer theme/design-system selection at scaffold time, or ship a sensible default (e.g. dark)?
• Do we want a "Open in GitHub Codespaces" badge in the engine README pointing at the starter?

Notes

Related: the engine repo's own .devcontainer/ and the Start DECKIO task can serve as a reference implementation, but the starter should target end users building decks, not engine development.

[DevSecNinja]

@lopezleandro03