chore(ci): add ACT guards to skip DockerHub steps in local act runs

act sets ACT=true automatically. Guards added:
- docker login: if: ${{ !env.ACT }}
- build outputs: type=docker (local load) when ACT, push-by-digest when CI
- digest export/upload: if: ${{ !env.ACT }}
- merge job: if: ${{ !env.ACT }}
- release-helm job (docker.yml): if: ${{ !env.ACT }}
- version-bump git push (docker.yml): wrapped in [ -z "$ACT" ] shell guard

Run locally with:
  ./bin/act -j build -W .github/workflows/docker.yml \
    -P ubuntu-latest=catthehacker/ubuntu:act-latest

.github/workflows/docker.yml

@@ -107,13 +107,15 @@ jobs:
           sed -i "s/^version: .*/version: $NEW_VERSION/" charts/trek/Chart.yaml
           sed -i "s/^appVersion: .*/appVersion: \"$NEW_VERSION\"/" charts/trek/Chart.yaml
 
-          # Commit and tag
-          git config user.name "github-actions[bot]"
-          git config user.email "github-actions[bot]@users.noreply.github.com"
-          git add package.json package-lock.json server/package.json client/package.json shared/package.json charts/trek/Chart.yaml
-          git commit -m "chore: bump version to $NEW_VERSION [skip ci]"
-          git tag "v$NEW_VERSION"
-          git push origin main --follow-tags
+          # Commit and tag (skipped when running locally with act)
+          if [ -z "$ACT" ]; then
+            git config user.name "github-actions[bot]"
+            git config user.email "github-actions[bot]@users.noreply.github.com"
+            git add package.json package-lock.json server/package.json client/package.json shared/package.json charts/trek/Chart.yaml
+            git commit -m "chore: bump version to $NEW_VERSION [skip ci]"
+            git tag "v$NEW_VERSION"
+            git push origin main --follow-tags
+          fi
 
   build:
     runs-on: ${{ matrix.runner }}
@@ -137,6 +139,7 @@ jobs:
       - uses: docker/setup-buildx-action@v3
 
       - uses: docker/login-action@v3
+        if: ${{ !env.ACT }}
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
@@ -147,18 +150,22 @@ jobs:
         with:
           context: .
           platforms: ${{ matrix.platform }}
-          outputs: type=image,name=mauriceboe/trek,push-by-digest=true,name-canonical=true,push=true
+          # act (local): load image into local Docker daemon instead of pushing.
+          # CI: push by digest to Docker Hub for multi-arch manifest assembly.
+          outputs: ${{ env.ACT == 'true' && 'type=docker' || 'type=image,name=mauriceboe/trek,push-by-digest=true,name-canonical=true,push=true' }}
           no-cache: true
           build-args: |
             APP_VERSION=${{ needs.version-bump.outputs.version }}
 
       - name: Export digest
+        if: ${{ !env.ACT }}
         run: |
           mkdir -p /tmp/digests
           digest="${{ steps.build.outputs.digest }}"
           touch "/tmp/digests/${digest#sha256:}"
 
       - name: Upload digest artifact
+        if: ${{ !env.ACT }}
         uses: actions/upload-artifact@v4
         with:
           name: digests-${{ env.PLATFORM_PAIR }}
@@ -167,6 +174,7 @@ jobs:
           retention-days: 1
 
   merge:
+    if: ${{ !env.ACT }}
     runs-on: ubuntu-latest
     needs: [version-bump, build]
     steps:
@@ -204,6 +212,7 @@ jobs:
         run: docker buildx imagetools inspect mauriceboe/trek:latest
 
   release-helm:
+    if: ${{ !env.ACT }}
     runs-on: ubuntu-latest
     needs: version-bump
     steps: