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/.prettierrc

@@ -0,0 +1,15 @@
+{
+  "semi": true,
+  "trailingComma": "es5",
+  "singleQuote": false,
+  "printWidth": 80,
+  "tabWidth": 2,
+  "useTabs": false,
+  "bracketSpacing": true,
+  "bracketSameLine": false,
+  "arrowParens": "avoid",
+  "endOfLine": "lf",
+  "quoteProps": "as-needed",
+  "jsxSingleQuote": false,
+  "proseWrap": "preserve"
+}