Fix image tag: strip leading v from release tag (vv1.1.0 -> v1.1.0)

mcp-grafana GitHub releases are tagged v1.1.0, so prefixing v$VER
produced vv1.1.0. Normalize the tag to v<semver> for the Monday
image cron.

.gitea/workflows/build.yaml

@@ -52,13 +52,16 @@ jobs:
           fi
           [ -n "$VER" ] || { echo "could not resolve upstream version"; exit 1; }
           echo "version=$VER" >> "$GITHUB_OUTPUT"
+          # Image tag strips a leading 'v' from the release tag (v1.2.3 -> v1.2.3),
+          # so the tag is always v<semver> regardless of upstream's tag style.
+          echo "tag=${VER#v}" >> "$GITHUB_OUTPUT"
           echo "Resolved grafana/mcp-grafana version: $VER"
 
       - name: Skip if already published
         id: skip
         run: |
-          if docker manifest inspect "$IMAGE:v${{ steps.ver.outputs.version }}" >/dev/null 2>&1; then
-            echo "Image $IMAGE:v${{ steps.ver.outputs.version }} already exists — nothing to do."
+          if docker manifest inspect "$IMAGE:v${{ steps.ver.outputs.tag }}" >/dev/null 2>&1; then
+            echo "Image $IMAGE:v${{ steps.ver.outputs.tag }} already exists — nothing to do."
             echo "skip=true" >> "$GITHUB_OUTPUT"
           else
             echo "skip=false" >> "$GITHUB_OUTPUT"
@@ -98,12 +101,13 @@ jobs:
         if: steps.skip.outputs.skip != 'true'
         run: |
           VER="${{ steps.ver.outputs.version }}"
+          TAG="${{ steps.ver.outputs.tag }}"
           docker build --build-arg MCP_GRAFANA_VERSION="$VER" \
-            -t "$IMAGE:v$VER" -t "$IMAGE:latest" .
+            -t "$IMAGE:v$TAG" -t "$IMAGE:latest" .
 
       - name: Push
         if: steps.skip.outputs.skip != 'true'
         run: |
-          VER="${{ steps.ver.outputs.version }}"
-          docker push "$IMAGE:v$VER"
+          TAG="${{ steps.ver.outputs.tag }}"
+          docker push "$IMAGE:v$TAG"
           docker push "$IMAGE:latest"