[TASK] Integrate C8Run into Release Train BPMN

[bkenez]

Related to

Epic: https://github.com/camunda/team-distribution/issues/693
Depends on: C8Run GHA workflows

RC Release

1. GitHub connector: c8run-preflight-check.yaml
2. GitHub connector: c8run-release.yaml (RC inputs)
3. On failure → Activity_1yhi0yt userTask (fallback)

Public Release

1. GitHub connector: c8run-release.yaml (public inputs)
2. GitHub connector: c8run-release-cleanup.yaml
3. On failure → Activity_0gayhob userTask (fallback)

QA

Already automated via Activity_1cnjz96 - no changes.

Notes

Artifacts URL deterministic: https://downloads.camunda.cloud/release/camunda/c8run/{version}/