feat(frontend): add Front/ — Vite/React frontend with backend pipeline integration

Mirror of design_agent_front/design-agent/ for shipping alongside backend.

Vite plugin (vitePluginPhaseZApi) endpoints :
  - POST /api/run   — spawn `python -m src.phase_z2_pipeline` with overrides
  - GET  /api/sample-mdx?mdx=03/04/05 — fixed sample MDX
  - GET  /frame-preview/{n} — figma preview thumbnails
  - GET  /data/runs/{run_id}/{path} — pipeline artifacts (final.html, step*.json, ...)

Env toggle forward (보고용) :
  PHASE_Z_ALLOW_RESTRUCTURE / PHASE_Z_ALLOW_REJECT / PHASE_Z_MAX_RANK=32

Components :
  - LeftMdxPanel (03/04/05 fix list + section tree)
  - SlideCanvas (iframe + slideOverrideCss prop for inline CSS inject)
  - FramePanel (label priority + confidence sort)
  - LayoutPanel

README with mermaid diagrams covering the 5-step demo flow.
node_modules / dist / .manus-logs / .env excluded via .gitignore.

Front/README.md

@@ -0,0 +1,44 @@
+# Design Agent Frontend
+
+React + Vite + TypeScript frontend.
+
+## 위치
+
+- `Front/` — 이 폴더
+- 원본 작업 위치 = `D:\ad-hoc\kei\design_agent_front\design-agent\` (로컬 dev)
+
+## 실행
+
+```
+cd Front/
+pnpm install
+pnpm dev
+```
+
+http://localhost:3000 에서 확인. `DESIGN_AGENT_ROOT` env 로 backend 경로 지정 가능.
+
+## 구조
+
+```
+Front/
+├── client/                React frontend (Vite root)
+│   └── src/
+│       ├── pages/
+│       ├── components/
+│       ├── services/
+│       └── ...
+├── server/                production express
+├── vite.config.ts         dev plugin + backend 연결
+└── ...
+```
+
+## Backend 연결 (vite.config.ts)
+
+Vite dev plugin 이 다음 endpoint 등록 :
+
+| Endpoint | 동작 |
+|---|---|
+| `POST /api/run` | MDX + overrides → backend pipeline spawn → run_id 반환 |
+| `GET /api/sample-mdx?mdx=...` | sample MDX serve |
+| `GET /frame-preview/{n}` | frame thumbnail |
+| `GET /data/runs/{run_id}/{path}` | pipeline 산출물 serve |