Add CI workflow and deployment guide

.github/workflows/ci.yml

@@ -0,0 +1,38 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  verify:
+    name: Lint and build
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version-file: .nvmrc
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Build
+        run: npm run build
+        env:
+          NEXT_PUBLIC_SUPABASE_URL: https://example.supabase.co
+          NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY: sb_publishable_placeholder