fix(release): allow promotion to read bound draft

[jeremi]

Summary\n\n- allow only the image-promotion job to access the exact nonpublic GitHub Release draft\n- update the existing exact permission-map test\n- leave release steps, artifact bytes, draft binding, and image reconciliation unchanged\n\n## Root cause\n\nPublication run 30713620744 failed on the promotion job's first GET of the bound draft with HTTP 403. The job had contents: read, while GitHub requires push-level contents access to retrieve a draft release. The preceding staging job had contents: write and successfully created and reconciled the same draft.\n\nThe failure happened before registry login. The v0.16.3 draft remains unpublished and exactly bound to candidate manifest f07f537323efde5de690c9388dc3e38b35379358d5350f2ba812fd72c77d6546, and both public v0.16.3 image tags remain absent.\n\n## Security scope\n\nThe additional permission is job-local. The promotion job still re-fetches and validates the exact draft before the first public image write, and it still copies an image only when the final tag is absent or accepts an existing exact digest. Checkout credentials remain disabled, and the job contains no repository, Release, asset, deletion, or publication mutation.\n\n## Verification\n\n- actionlint .github/workflows/release.yml\n- 101 focused release workflow, guard, and gate-inventory tests\n- live gate inventory: 151 gates passed\n- git diff --check\n- independent release diagnosis and security-focused diff review

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