docs(spec): convert due-date stub into dogfood-feedback collection

Reframe the file as a living register for in-flight dogfood feedback
rather than a single-feature stub. Each item carries a status label
(raw / drafting / ready-for-spec / promoted / rejected) and a fixed
six-slot template (관찰 / 제안 방향 / 결정 대기 / 가설·측정 / 범위 /
영향). Items graduate to their own spec file once mature; the entry
here then collapses to a one-line link.

- F1: Due-date 추출 (drafting) — content from the previous stub
  normalized to the new template.
- F2: 태그 클릭 = 즉시 삭제 + undo 부재 (raw) — NoteCard.tsx:110
  binds chip onClick to removeTag, no confirm or undo, and there is
  no "filter by tag" affordance to match the user's mental model.
  Direction: split click=filter, ✕-icon=remove with 5s undo toast.

README docs map updated to point at the new path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -163,7 +163,7 @@ inkling.md         원본 제품 브리프 v1.4
 | 심리학 전략 | `docs/superpowers/strategy/strategy.md` | 행동 변화 모델, 회복 친화 스트릭 |
 | Dogfooding 전략 | `docs/superpowers/strategy/dogfood-strategy.md` | 2주 자기 dogfood 운영안 |
 | 슬라이스 설계 | `docs/superpowers/specs/2026-04-24-inkling-vertical-slice-design.md` | v0.4 spec, 부하 전달 결정의 출처 |
-| Due Date 추출 (stub) | `docs/superpowers/specs/2026-04-25-due-date-extraction-design.md` | 슬라이스 dogfood 후 정식화할 후속 spec 골격 |
+| Dogfood 피드백 | `docs/superpowers/specs/2026-04-25-dogfood-feedback.md` | 슬라이스 dogfood 중 발견된 본인 피드백 수집 (living document) |
 | 구현 계획 | `docs/superpowers/plans/2026-04-24-inkling-vertical-slice.md` | 33-task TDD 플랜 |
 | 핸드오프 | `docs/handoff/2026-04-25-linux-to-windows.md` | Linux→Windows 전환 메모 |