[Feature] Use GitHub-native generated release notes

[TorinAsakura]

Task

• Closes [Feature] Replace custom changelog flow with GitHub-native release notes #743

Contract

• Release note bodies are repository-scoped public product notes.
• Package tags and versions identify the released artifact; they do not imply an internal workspace-scoped changelog body.
• Workspace/path filtering from the legacy changelog path is intentionally removed from the active publish path.

How to Verify

Main Scenario

1. Context: post-merge publish workflow.
   Action: merged PR publish reaches the release path.
   Expected result: the workflow no longer runs the legacy changelog generate action, and yarn release create asks GitHub to generate release notes through the GitHub Releases API before creating each release.

Additional Scenario

1. Context: release plugin unit coverage.
   Action: run yarn test unit release-create --test-reporter=tap.
   Expected result: release note generation uses package-specific previous tags and a target commitish for new release tags.

Proofs

• yarn test unit release-create --test-reporter=tap
• Targeted yarn typecheck and yarn lint for changed release files
• yarn workspace @atls/code-github build
• yarn workspace @atls/yarn-plugin-release build
• yarn workspace @atls/yarn-cli build
• cmp -s yarn/cli/dist/yarn.mjs .yarn/releases/yarn.mjs
• yarn raijin:check
• yarn check

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