Added web app building thing.

.gitea/workflows/build-web-app.yaml

@@ -0,0 +1,17 @@
+name: Build Web App
+on:
+  push:
+    paths:
+      - 'web-app/**'
+      - '.gitea/workflows/build-web-app.yaml'
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22.x'
+      - run: npm ci
+      - run: npm run build --if-present
+      - run: npm test