fix: centralize release auto-merge - #3

Why

Release Please pull requests were excluded from the required organization auto-merge workflow, leaving product release workflows to merge directly. That conflicts with organization rulesets and blocked SQLBuild release PR #331.

Changes

• Request squash auto-merge for trusted same-repository Release Please pull requests.
• Keep release-specific validation in product workflows while making the organization workflow the single auto-merge owner.
• Document that product release workflows must create and update release branches with the delivery App token so GitHub emits the required pull request events.

Verification

• git diff --check
• Confirmed draft and fork PR exclusions remain unchanged.
• Confirmed required checks and repository rules remain authoritative before merge.