Add just docker-push, use justfile for CI Docker steps

Add docker-push recipe with configurable DOCKER_REPO (defaults to
"taskflow", overridable via env var). CI now uses just docker-build
and just docker-push instead of the docker/build-push-action.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bricef

.github/workflows/ci.yml

@@ -31,8 +31,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+      - uses: extractions/setup-just@v2
 
       - name: Log in to Docker Hub
         uses: docker/login-action@v3
@@ -41,12 +40,9 @@ jobs:
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       - name: Build and push
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          push: true
-          tags: |
-            ${{ secrets.DOCKERHUB_USERNAME }}/taskflow:latest
-            ${{ secrets.DOCKERHUB_USERNAME }}/taskflow:${{ github.sha }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+        env:
+          DOCKER_REPO: ${{ secrets.DOCKERHUB_USERNAME }}/taskflow
+        run: |
+          just docker-build
+          just docker-push latest
+          just docker-push ${{ github.sha }}

justfile

@@ -1,3 +1,6 @@
+# Docker image repository (override with DOCKER_REPO env var or `just --set DOCKER_REPO ...`)
+DOCKER_REPO := env("DOCKER_REPO", "taskflow")
+
 # Default: list available recipes
 default:
     @just --list
@@ -51,6 +54,11 @@ run:
 docker-build:
     docker build -t taskflow .
 
+# Push Docker image to registry
+docker-push tag="latest":
+    docker tag taskflow {{DOCKER_REPO}}:{{tag}}
+    docker push {{DOCKER_REPO}}:{{tag}}
+
 # Run with Docker Compose
 docker-up:
     docker compose up -d