New Project: create-shopify-firebase-app

**GitHub link:** https://github.com/mksd0398/create-shopify-firebase-app

**What it is (2-3 sentences):**
An MIT-licensed CLI that scaffolds an embedded Shopify app running entirely on Firebase — Hosting for the frontend, gen-2 Cloud Functions for OAuth, the Admin API, webhooks and the storefront app proxy, and Firestore for session storage. One command takes you from nothing to a deployed, installable Shopify app, including creating and provisioning the Firebase project. It is positioned as the Firebase alternative to Shopify official Remix/React Router template, which assumes a Node server plus Postgres.

**Why would Firebase developers be interested?**
Shopify app development is a sizeable ecosystem whose official tooling assumes a long-running Node server and a relational database, so Firebase is not an obvious path and there is little material showing how to do it well. This project is a worked example of the serverless equivalent: session-token (JWT) verification on gen-2 Functions, Firestore as the OAuth session store with deny-all rules since access is admin-SDK only, HMAC verification for webhooks and app proxy, and Hosting rewrites mapping clean paths onto individual functions. It also makes a concrete cost argument for Firebase — the free tier covers a meaningful number of installed merchants before Blaze usage begins.

**Have you added `.opensource/project.json`?**
Yes — added at [`.opensource/project.json`](https://github.com/mksd0398/create-shopify-firebase-app/blob/master/.opensource/project.json) with `platforms: ["Web"]`.

**Note on the setup docs:** `docs/configure-repo.md` currently instructs contributors to add their repo to `additional-projects.json`, but that file no longer exists in this repository — the live registry appears to be `config/additional_projects.json`. Happy to open a PR against whichever is correct if that is preferred over an issue.

Start with the submitted .opensource/project.json and read docs/configure-repo.md alongside config/additional_projects.json to verify the current project-registration workflow. Confirm the correct registry location and contributor guidance, then ensure the create-shopify-firebase-app entry can be processed by the site without relying on the obsolete additional-projects.json path.

Written by the indexing model from the issue text.