docs(backlog): reconcile protected merge evidence

[aatuh]

Backlog ticket

• Ticket ID: PRG-003
• One backlog ticket only; unrelated work was excluded.

Final commit

• PR title uses conventional commit syntax.
• Final squash commit body will include Refs: PRG-003.
• Breaking change: not applicable.

Verification

PASS GOWORK=off GOTOOLCHAIN=local make docs-check

Classification

• Compatibility: No public effect.
• Security: No new trust boundary or sensitive-data handling.
• Documentation/release notes: Backlog evidence reconciled; release notes not applicable.
• Generated files: none.
• Benchmarks: not applicable.
• Migration: none.

Only proven protected merges are marked [x]: REL-000A (#68), PRG-001 (#70), PRG-002 (#71), and EXT-001 (#72). PRG-003 itself remains [pr] until this PR merges.