add workflow

Author: samfreund

.github/workflows/build.yml

@@ -91,7 +91,32 @@ jobs:
         run: |
           ./gradlew build
           ./gradlew clean
-
+  typecheck-client:
+    name: "Typecheck Client"
+    runs-on: ubuntu-24.04
+    steps:
+      # Checkout code.
+      - name: Checkout code
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+      - name: Fetch tags
+        run: git fetch --tags --force
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - name: Setup Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: pnpm
+          cache-dependency-path: photon-client/pnpm-lock.yaml
+      - name: Typecheck Client
+        working-directory: photon-client
+        run: |
+          pnpm install
+          pnpm type-check
   playwright-tests:
     name: "Playwright E2E tests"
     runs-on: ubuntu-24.04