fix(release): draft PR description generator and milestone deliverable resolution

[dan-petty]

Description

Fix the draft PR description generator (devops release pr) to:

1. Automatically query target milestone issues via run_gh rate limiter and format under ### Target Milestone Deliverables with fallback to git commit log.
2. Discard stale duplicated changelog notes when extracted notes match the previous release section.
3. Update quality gate checklist to authoritative 10-Gate CI suite with dynamic draft checkbox states.

Acceptance Criteria

• Milestone issues queried and displayed in PR body.
• Stale duplicate changelog detection and fallback.
• Authoritative 10-Gate CI checklist with dynamic draft checkboxes.
• Full unit test coverage and 100% passing CI suite.

[dan-petty]

Resolved and merged in PR #219 into release/v0.2.19.