[infra] Gate nightly publishing and summarize artifacts (#58)

* [infra] Gate nightly publishing and summarize artifacts

Keep scheduled builds on Actions while allowing release branches to create protected draft releases with durable verification evidence.

* [infra] Clarify nightly workflow permissions

Document the elevated scopes and normalize the release archive variable for readability.

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Co-authored-by: Alexander Poddubny <143108850+nv-apoddubny@users.noreply.github.com>

Author: vikuznetsov-nvidia