fix(ci): optimize docker build — single platform, remove QEMU (#8)

- Remove QEMU setup (no ARM cross-compilation needed)
- Build only linux/amd64 (target deployment arch)
- Reduces build time from 35+ min to ~10-15 min
- Reduce timeout back to 30 min

Co-authored-by: Sebastian Noe <sebastian.schneider@boxine.de>

.github/workflows/docker-publish.yml

@@ -10,7 +10,7 @@ permissions: {}
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
-    timeout-minutes: 60
+    timeout-minutes: 30
     permissions:
       contents: read
       packages: write
@@ -21,9 +21,6 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@29109295f81e9208d7d86ff1c6c12d2833863392 # v3.6.0
-
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2 # v3.10.0
 
@@ -60,7 +57,7 @@ jobs:
         with:
           context: .
           push: true
-          platforms: linux/amd64,linux/arm64
+          platforms: linux/amd64
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha