Why: close the task card inside its own PR so landing it needs no post-merge backfill or separate close PR.
Evidence: .task/feature-docker-test-image.md -> .task/archive/feature-docker-test-image.md; status 已完成(合入前闭合); PR #645https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/645.
Impact: task metadata only; the card is archived within PR #645 and lands with its merge commit.
Refs: task.sh close --self