openapi: align asset download/export 202 status enum with runtime + sibling schemas

CodeRabbit caught a vocabulary mismatch: the two new 202 response schemas
declared `[pending, running, completed, failed]` while the rest of the same
spec uses `[created, running, completed, failed]` for the identical task
lifecycle (download/export progress WebSocket events, /api/tasks, TaskEntry,
TaskResponse — 4 sites total). Cloud's runtime emits `created` on initial
creation (AssetDownloadResponseStatusCreated; task.Status sourced from the
DB enum whose initial value is Created). `pending` would have introduced a
fifth, contradictory vocabulary for the same lifecycle and pushed the spec
further from the implementation it is meant to align with.

Followup tracked separately: extract a shared TaskStatus enum so all five
sites move in lockstep instead of needing per-site edits.

.github/workflows/backport_release.yaml

@@ -458,41 +458,6 @@ jobs:
 
           echo "Released ${NEW_VERSION} on ${RELEASE_BRANCH}."
 
-      - name: Delete remote source branch
-        env:
-          GH_TOKEN:        ${{ steps.app-token.outputs.token }}
-          REPO:            ${{ github.repository }}
-          SOURCE_BRANCH:   ${{ steps.resolve.outputs.source_branch }}
-          SOURCE_COMMIT:   ${{ inputs.commit }}
-          RELEASE_BRANCH:  ${{ steps.latest.outputs.release_branch }}
-          DEFAULT_BRANCH:  ${{ github.event.repository.default_branch }}
-        run: |
-          set -euo pipefail
-
-          # Belt-and-braces: the resolve step already refuses the default branch,
-          # but never delete the default or the release branch under any
-          # circumstances.
-          if [[ "${SOURCE_BRANCH}" == "${DEFAULT_BRANCH}" || "${SOURCE_BRANCH}" == "${RELEASE_BRANCH}" ]]; then
-            echo "::error::Refusing to delete '${SOURCE_BRANCH}' (matches default or release branch)."
-            exit 1
-          fi
-
-          # Delete the source branch on origin, but only if its tip is still the
-          # SHA we released from. If someone pushed new commits to it after we
-          # resolved it, leave it alone — those commits would be silently lost.
-          current_tip="$(git ls-remote origin "refs/heads/${SOURCE_BRANCH}" | awk '{print $1}')"
-          if [[ -z "${current_tip}" ]]; then
-            echo "Source branch '${SOURCE_BRANCH}' no longer exists on origin; nothing to delete."
-            exit 0
-          fi
-          if [[ "${current_tip}" != "${SOURCE_COMMIT}" ]]; then
-            echo "::warning::Source branch '${SOURCE_BRANCH}' tip (${current_tip}) no longer matches released commit (${SOURCE_COMMIT}). Leaving it in place."
-            exit 0
-          fi
-
-          git push origin --delete "refs/heads/${SOURCE_BRANCH}"
-          echo "Deleted remote branch '${SOURCE_BRANCH}'."
-
       - name: Summary
         if: always()
         env: