[FEATURE] Smoke-test dispatch: trigger promote-release for final; wait on CI for RC

[c-vigo]

Description

Update the smoke-test repository-dispatch workflow so final releases dispatch downstream promote-release.yml (publish release, merge PR, cleanup RC tags) instead of only merging the release PR; and so RC triggers verify release-PR CI but do not merge to main.

Problem statement

• Issue [BUG] promote-release validate step uses API endpoint that cannot find draft releases #507 / PR fix: resolve draft releases in promote-release validation #510 fixed draft-release handling in promote-release.yml.
• Today assets/smoke-test/.github/workflows/repository-dispatch.yml runs merge-release-pr for both RC and final: it enables auto-merge and polls.
• Downstream release.yml creates a draft final release; nobody publishes it, so the release stays draft.
• Upstream .github/workflows/promote-release.yml requires a published (non-draft, non-prerelease) downstream final release before it proceeds — so automation fails unless someone publishes manually.
• For RC, merging the release PR to main on every candidate is unnecessary; the branch is recreated on the next dispatch.

Proposed solution

Behavior split by release_kind:

Common path (RC + final): existing steps through trigger-release unchanged in intent; then replace terminal merge behavior as below.

1. Remove the merge-release-pr job.
2. Add wait-release-pr-ci (RC + final): after trigger-release, poll required checks on the release PR (gh pr checks); succeed when green; fail on failure or timeout (e.g. 30 min). For RC this is terminal — PR stays open.
3. Add trigger-promote-release (final only): if: needs.validate.outputs.release_kind == 'final'; repository-dispatch promote-release.yml on dev with version=$BASE_VERSION; same dispatch-and-poll pattern as trigger-release / trigger-prepare-release. Downstream promote-release validates draft + PR, publishes release, merges PR, cleans RC tags.
4. Update summary and notify-failure: depend on wait-release-pr-ci and trigger-promote-release; treat skipped trigger-promote-release on RC as success, not failure.

Docs: Update docs/CROSS_REPO_RELEASE_GATE.md — receiver triggers promote-release for final; RC path no longer merges.

Scope: assets/smoke-test/.github/workflows/repository-dispatch.yml + docs/CROSS_REPO_RELEASE_GATE.md. Do not change upstream or workspace-template promote-release.yml in this issue.

Alternatives considered

• Duplicate publish/merge/cleanup logic in repository-dispatch.yml — rejected (DRY; dogfood promote-release template).

Additional context

• Workspace template already ships assets/workspace/.github/workflows/promote-release.yml via init-workspace.sh.
• Prerequisite: PR fix: resolve draft releases in promote-release validation #510 merged and deployed to the smoke-test repo before exercising this change end-to-end.
• Related: [BUG] promote-release validate step uses API endpoint that cannot find draft releases #507 (draft release API), fix: resolve draft releases in promote-release validation #510 (fix).

Impact

• Unblocks upstream promote-release by publishing the downstream final release automatically.
• RC flow stops merging prematurely; aligns with cross-repo gate contract for pre-releases.

Changelog category: Changed

• TDD compliance (see .cursor/rules/tdd.mdc)