Add build workflow

.gitea/workflows/build.yml

@@ -0,0 +1,24 @@
+name: Build
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: checkout code
+        uses: actions/checkout@v3
+      - name: setup node
+        uses: actions/setup-node@v3
+        with:
+          node-version: 24
+
+      - name: install dependencies
+        run: npm ci
+      - name: build extension for Firefox
+        run: npm run build