* security: harden release workflows against secret leakage
Verify trusted refs before secret-bearing jobs, narrow secret scope, pin key actions, and remove the opencode agents workflow to reduce workflow attack surface.
* security: drop third-party action pinning
Keep the trusted ref gates and narrower secret exposure, but revert external GitHub Actions back to their tagged versions to avoid broad supply-chain hardening changes in this PR.
* security: scope trusted release refs to dev
Update the workflow trust gates to validate tags and manual refs only against origin/dev, matching this repository's actual protected branch layout.
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Co-authored-by: src-opn <src-opn@users.noreply.github.com>