docs(IMP-19): zone ratio reference + cross-link -- documented-axis close

Stage 5 commit for IMP-19 (gitea #19) — docs-only, no runtime surface.

- new: docs/architecture/IMP-19-ZONE-RATIO-REFERENCE.md (header + A1 consumer
  + A2 producer + A3 Phase Z solver delta + A4 IMP-09 boundary + A5
  re-activation gate / GR1-GR4).
- update: PHASE-Z-IMPLEMENTATION-ISSUE-BACKLOG.md — IMP-19 row pending ->
  documented + reference doc link; IMP-09 row carries soft back-link to the
  IMP-19 reference doc.
- update: PHASE-Q-INSIGHT-TO-22STEP-MAP.md §3 I4 row — prepend IMP-19 anchor
  + reference doc link (step/classification preserved).

Guardrails (Stage 1/2 binding contract): src/ untouched, no role-based
["배경","본심"] hardcoding into Phase Z, IMP-09 solver ownership preserved,
soft-link integrity holds. IMP-19 remains dormant until the A5 gate fires.

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

docs/architecture/PHASE-Z-IMPLEMENTATION-ISSUE-BACKLOG.md

@@ -50,7 +50,7 @@
 | IMP-06 | B-1 Zone-section override | Step 6 + input Step 1, 22 | §2 B-1 새로 만들기 (backend path) | medium | CLI 인자 + composition planner override path 신설 | Kei composition / Phase R' frame 보조 회귀 X / override 적용 시 composition_unit schema 정합 + trace | soft link: IMP-04 (frame 후보 ↑ 시 override 의미 ↑) | implemented |
 | IMP-07 | B-2 Edited HTML → MDX reverse path | Step 22 + Step 1, 2 | §2 B-2 새로 만들기 (backend path) | medium | frontend edited HTML → backend → MDX 변환 → pipeline 재진입 (글벗 `html_to_slide_mdx` 참조) | AI/Kei reverse 회귀 X / 재진입 후 step02 정합 + visual_check 통과 | hard link: IMP-02 (A-1 normalize schema 와 reverse path schema 정합 필요) | implemented |
 | IMP-08 | B-3 Sub-section drag drop | Step 3 | §2 B-3 새로 만들기 (backend schema) | ↓ low | Phase Z `section_id` schema 확장 (sub_sections 단위 매핑) | AI/Kei schema 회귀 X / backward compatible / step03 trace | hard link: IMP-02 (A-1 normalize sub_sections schema 의존) | implemented |
-| IMP-09 | B-4 다른 layout zone-geometry | Step 8 | §2 B-4 새로 만들기 (backend layout) | ↓ low | `build_layout_css` 분기 확장 (top-1-bottom-2 / left-1-right-2 / grid-2x2 등) | Kei `build_containers_type_b` 회귀 X / step08 trace | none | implemented |
+| IMP-09 | B-4 다른 layout zone-geometry | Step 8 | §2 B-4 새로 만들기 (backend layout) | ↓ low | `build_layout_css` 분기 확장 (top-1-bottom-2 / left-1-right-2 / grid-2x2 등) | Kei `build_containers_type_b` 회귀 X / step08 trace | soft back-link: IMP-19 ([reference doc](IMP-19-ZONE-RATIO-REFERENCE.md) — Phase O block-level pattern reference, no runtime integration) | implemented |
 | IMP-10 | D-1 filtered_section_reasons UI | Step 20, 22 | §2 D-1 frontend 신규 | ↓ low | frontend UI — backend artifact read-only 표시 | AI/Kei UI 회귀 X / backend artifact read-only | none | implemented |
 | IMP-11 | D-2 Frame min_height 표시 | Step 22 | §2 D-2 새로 만들기 (frontend hint + catalog 참조) | ↓ low | frontend UI — frame contract `min_height_px` read-only + resize hint | AI/Kei UI 회귀 X / catalog 참조 + resize limit | none | implemented |
 
@@ -67,7 +67,7 @@
 | IMP-16 | B-2 verification 보조 axis | Step 1, 2, 14, 21, 22 | §3 H3 Reference Only | ↓ low | B-2 reverse path 의 verification 보조. main reverse path 는 IMP-07, 본 issue 는 text/visual/trace 검증 layer | AI/Kei verification 회귀 X / utility deterministic | hard link: IMP-07 (B-2 main 활성 시점 의미) | implemented |
 | **IMP-17** | **AI repair fallback infra** (**carve-out — normal path 밖**) | Step 12, 16, 17 | §3 G3 | (별 axis priority — pending) | [carve-out boundary + activation gate](IMP-17-CARVE-OUT.md) (3-cond AND: User GO ∧ B4 frame_selection evidence ∧ IMP-04/05 live — full def in u2 doc) — `httpx` + SSE streaming + retry + JSON parse pattern reference — light_edit / restructure proposal | **normal path AI 호출 0 — 본 axis = fallback only, normal path 와 분리 설계** / Kei persona 단절 (Phase Q 자산과 단절) | soft link: IMP-04 + IMP-05 (catalog 확장 + V4 fallback 활성 시 의미) | documented (deferred) |
 | IMP-18 | I3 SVG 좌표 보강 | Step 0, 9 | §3 Reference Only | ↓ low | `renderer._preprocess_svg_data` 패턴 reference — frame_partials SVG 좌표 사전 박힘 — [gap report](IMP-18-SVG-GAP-REPORT.md) | Phase R' (renderer.py) 회귀 X | soft link: IMP-04 (frame_partials 등록 후 의미 ↑) | documented |
-| IMP-19 | I4 zone 비중 분배 | Step 8 | §3 Reference Only | ↓ low | `renderer._group_blocks_by_area` 패턴 reference — zone-level ratio 분배 | Phase O 컨테이너 회귀 X / 직접 통합 X | soft link: IMP-09 (zone 비중 분배 영역 공유) | pending |
+| IMP-19 | I4 zone 비중 분배 | Step 8 | §3 Reference Only | ↓ low | `renderer._group_blocks_by_area` 패턴 reference — zone-level ratio 분배 — [reference doc](IMP-19-ZONE-RATIO-REFERENCE.md) | Phase O 컨테이너 회귀 X / 직접 통합 X | soft link: IMP-09 (zone 비중 분배 영역 공유) | documented |
 | IMP-20 | H2 frame contract validation | Step 10 | §3 Reference Only | ↓ low | `content_verifier.verify_structure` pattern reference — Phase Z frame contract 검증 pattern | Phase Q `REQUIRED_PATTERNS` 값 회귀 X / Phase Z 자체 pattern dict 설계 | soft link: IMP-04 (확장 catalog 적용 시 검증 범위 확대) | pending |
 
 > **IMP-15 child issues note (#45–#49)** — IMP-15 (Step 14 visual_check 보강) is the parent row; child sub-axes were tracked as separate Gitea issues and are not given standalone backlog rows. Children: #45 (e9b3d2e), #46 (2827622), #47 (535c484), #48 (614c533), #49 (verification-only). Per INTEGRATION-AUDIT-01 §10.3 footnote option to avoid double-counting under IMP-15.