fix(ci): skip GitHub release creation when tag already exists

Multiple pipeline runs for the same base version produce identical
release tags, causing E422. Check if release exists before creating.

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

.github/workflows/pipeline.yml

@@ -164,10 +164,15 @@ jobs:
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          gh release create "v${{ steps.base-version.outputs.version }}" \
-            --title "v${{ steps.base-version.outputs.version }}" \
-            --generate-notes \
-            --latest
+          TAG="v${{ steps.base-version.outputs.version }}"
+          if gh release view "$TAG" >/dev/null 2>&1; then
+            echo "Release $TAG already exists — skipping"
+          else
+            gh release create "$TAG" \
+              --title "$TAG" \
+              --generate-notes \
+              --latest
+          fi
 
   update-builder:
     name: Update CI Builder Image