ci: build single binary and publish GHCR image on main/dev

Test builds ./cmd/openfsd only. Docker job builds on PRs and pushes
:latest, :dev, and sha tags on push to main and dev.

.github/workflows/ci.yml

@@ -1,13 +1,16 @@
 name: CI
 on:
   push:
-    branches: [main]
+    branches: [main, dev]
   pull_request:
   schedule:
     # Weekly stress baselines (optional; does not gate PRs on latency).
     - cron: "0 6 * * 1"
   workflow_dispatch:
 
+permissions:
+  contents: read
+
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -20,8 +23,55 @@ jobs:
         run: go test -race -count=1 ./...
       - name: Coverage floor ≥80% (exclude cmd/)
         run: bash scripts/check-coverage.sh 80
-      - name: Build binaries
-        run: go build -o /tmp/openfsd ./cmd/openfsd && go build -o /tmp/openfsd-web ./cmd/openfsd-web
+      - name: Build binary
+        run: go build -o /tmp/openfsd ./cmd/openfsd
+
+  docker:
+    # Build and publish the single openfsd image on every push to main/dev.
+    # PRs only build (no push) to verify the Dockerfile stays green.
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GitHub Container Registry
+        if: github.event_name == 'push'
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            # Always publish branch tip tags; main also updates :latest.
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
+            type=raw,value=dev,enable=${{ github.ref == 'refs/heads/dev' }}
+            # While primary work is on dev, keep :latest in sync with dev too.
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/dev' }}
+            type=sha,prefix=sha-
+            type=ref,event=branch
+            type=ref,event=pr
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          push: ${{ github.event_name == 'push' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
 
   stress:
     # Optional: scheduled or manual. Never fails on absolute latency thresholds.