build(Docker/ci): get rid of running partial build locally

this is now handled fully inside Docker.

exception for "test_docker" job in "main-docker"
-> it seems that one needs to be there still, since it runs Playwright tests from outside the container

.github/workflows/main-docker.yml

@@ -151,16 +151,6 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-
-      - name: Set up node & dependencies
-        uses: actions/setup-node@v4
-        with:
-          node-version: 20
-          cache: "npm"
-      - run: npm ci
-      - name: Run the TypeScript build
-        run: npx tsc
-
       - name: Login to GHCR
         uses: docker/login-action@v3
         with: