fix(release): resolve in-toto attestation UUID in wait-for-chains

[infernus01]

Changes

Summary

• Fix wait-for-chains inline task to resolve the correct Rekor
  UUID (in-toto attestation) instead of the per-image signature
  (hashedrekord) entry
• Port of fix: resolve in-toto attestation UUID in wait-for-chains pipeline#10363 to this repo

Problem

The chains.tekton.dev/transparency annotation on the publish-images
TaskRun points at a hashedrekord Rekor entry. This entry contains a
bare signature with no .Attestation payload, so the release notes
verification commands (rekor-cli get --uuid ... | jq -r .Attestation)
return empty. Verified broken on: chains v0.28.1, chains v0.29.0,
pruner v0.4.0, pruner v0.4.1.

Fix

Instead of trusting the transparency annotation, the task now:

1. Reads the IMAGES result from the publish-images TaskRun
2. Searches the Rekor index for all entries matching the first
   image digest
3. Selects the entry with body kind intoto
4. Falls back to the annotation-based approach if not found

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• pre-commit Passed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

/kind bug

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.28%. Comparing base (05bebae) to head (c40cd29).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #378   +/-   ##
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  Coverage   50.28%   50.28%           
=======================================
  Files          19       19           
  Lines        2118     2118           
=======================================
  Hits         1065     1065           
  Misses        921      921           
  Partials      132      132           

Flag	Coverage Δ
unit-tests	50.28% <ø> (ø)

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