CI: inline build job and use mode=min GHA cache

The reusable workflow from dockette/.github hardcodes
cache-to:type=gha,mode=max which fails for large images like coder
(docker/buildx#841). The GHA cache API returns HTML error pages when
hitting size/rate limits, causing "buildx failed with: </body></html>".

Inline the build steps so we can control cache settings. Use the
default mode=min which only caches final layers, avoiding the issue.

https://claude.ai/code/session_01WY1ytdnf8Hrx3p7fnmZCUr

Author: claude

.github/workflows/docker.yml

@@ -38,11 +38,30 @@ jobs:
   build:
     name: "Build"
     needs: test
-    uses: dockette/.github/.github/workflows/docker.yml@master
-    secrets: inherit
-    with:
-      image: "dockette/coder"
-      tag: "fx"
-      context: "fx"
-      platforms: "linux/amd64"
-      push: ${{ github.ref == 'refs/heads/master' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v4
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
+
+      - name: Build and push
+        uses: docker/build-push-action@v7
+        with:
+          context: ./fx
+          file: ./fx/Dockerfile
+          push: ${{ github.ref == 'refs/heads/master' }}
+          tags: dockette/coder:fx
+          platforms: linux/amd64
+          cache-from: type=gha
+          cache-to: type=gha