fix(#2491): finish todos/done -> todos/completed rename (14 stale refs) + guard (#2626)

* test(#2491): add todos/done rename under-sweep guard

* fix(#2491): finish todos/done -> todos/completed rename (14 stale refs)

* chore(#2491): backfill changeset pr to 2626

* test(#2491): fix lint-legacy-dir-name + allow-test-rule-refs (split legacy token, add issue ref)

docs/ja-JP/ARCHITECTURE.md

@@ -500,7 +500,7 @@ UI-SPEC.md (per phase) ───────────────────
 │       └── SUMMARY.md
 ├── todos/
 │   ├── pending/            # キャプチャされたアイデア
-│   └── done/               # 完了済みtodo
+│   └── completed/          # 完了済みtodo
 ├── threads/               # 永続コンテキストスレッド（/gsd-thread から）
 ├── seeds/                 # 将来に向けたアイデア（/gsd-capture --seed から）
 ├── debug/                  # アクティブなデバッグセッション

docs/ja-JP/USER-GUIDE.md

@@ -853,7 +853,7 @@ All subagent/executor commits MUST use `--no-verify`.
   reports/                # Session reports (from /gsd-pause-work --report)
   todos/
     pending/              # Captured ideas awaiting work
-    done/                 # Completed todos
+    completed/             # Completed todos
   debug/                  # Active debug sessions
     resolved/             # Archived debug sessions
   spikes/                 # Feasibility experiments (from /gsd-spike)