Retire the member close-and-migrate path

[sameera]

Retire the member close-and-migrate path once the hub-born flow is proven: remove the member-mode close choreography, delete the close-migration helper (skill + lib), and relocate any in-flight member-queue entries into the hub as a one-time cutover — after which the distillation-PR merge is the only cleanup anywhere in the system.

Meta

• feature: docs/features/multi-repo-workspaces
• estimate: S
• candidate stories: Remove the member close-and-migrate path; Delete the close-migration helper; One-time relocation of in-flight member entries
• source: decomposition of "Refactor multi-repo workspaces around PR-driven delivery (hub-born queue)" (2026-07-20)
• migrated: 2026-08-01, from the per-feature backlog file retired by Backlog Stubs Become GitHub Issues #185