Add CI workflow for app builds

Author: ymxlx

.github/workflows/ci.yml

@@ -0,0 +1,35 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    name: Typecheck and build
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [20, 22]
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Typecheck
+        run: npm run lint
+
+      - name: Build
+        run: npm run build

README.md

@@ -3,6 +3,7 @@
 ![TypeScript](https://img.shields.io/badge/TypeScript-5.8-3178c6)
 ![three.js](https://img.shields.io/badge/three.js-r184-000000)
 ![React 19](https://img.shields.io/badge/React-19-61dafb)
+[![CI](https://github.com/yehudalevy-collab/proofs-of-nine/actions/workflows/ci.yml/badge.svg)](https://github.com/yehudalevy-collab/proofs-of-nine/actions/workflows/ci.yml)
 
 The number **9**, written by itself in infinite mathematics.