fix(ci): pass Go image tag from build to gitops via artifact

github.event.workflow_run.head_branch is not populated for tag pushes
in Gitea Actions, causing the image tag to resolve to empty (-go suffix
with no version). Fix: build-go uploads the full image reference as a
one-line artifact; gitops-update downloads it via download-artifact@v4
with run-id from the workflow_run event.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/build.yaml

@@ -63,3 +63,11 @@ jobs:
             --build-arg BUILD_DATE=$(date -u +%Y-%m-%dT%H:%M:%SZ) \
             -t $IMAGE go/
           docker push $IMAGE
+          echo "$IMAGE" > /tmp/go-image-tag.txt
+
+      - name: Upload Go image tag for gitops workflow
+        uses: actions/upload-artifact@v4
+        with:
+          name: go-image-tag
+          path: /tmp/go-image-tag.txt
+          retention-days: 1

.gitea/workflows/gitops-update.yaml

@@ -58,16 +58,22 @@ jobs:
             -o /usr/local/bin/uh-cli
           chmod +x /usr/local/bin/uh-cli
 
+      - name: Download image tag artifact (workflow_run trigger)
+        if: github.event_name == 'workflow_run'
+        uses: actions/download-artifact@v4
+        with:
+          name: go-image-tag
+          run-id: ${{ github.event.workflow_run.id }}
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Resolve image tag
         id: resolve
         run: |
           if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
-            GIT_TAG="${{ inputs.tag }}"
+            IMAGE="gitea.home.hrajfrisbee.cz/${{ github.repository }}:${{ inputs.tag }}-go"
           else
-            # workflow_run: use the ref name of the triggering workflow (the pushed git tag).
-            GIT_TAG="${{ github.event.workflow_run.head_branch }}"
+            IMAGE="$(cat go-image-tag.txt)"
           fi
-          IMAGE="gitea.home.hrajfrisbee.cz/${{ github.repository }}:${GIT_TAG}-go"
           echo "image=${IMAGE}" >> "$GITHUB_OUTPUT"
           echo "Resolved image: ${IMAGE}"