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/client/src/components/ui/scroll-area.tsx

@@ -0,0 +1,56 @@
+import * as React from "react";
+import * as ScrollAreaPrimitive from "@radix-ui/react-scroll-area";
+
+import { cn } from "@/lib/utils";
+
+function ScrollArea({
+  className,
+  children,
+  ...props
+}: React.ComponentProps<typeof ScrollAreaPrimitive.Root>) {
+  return (
+    <ScrollAreaPrimitive.Root
+      data-slot="scroll-area"
+      className={cn("relative", className)}
+      {...props}
+    >
+      <ScrollAreaPrimitive.Viewport
+        data-slot="scroll-area-viewport"
+        className="focus-visible:ring-ring/50 size-full rounded-[inherit] transition-[color,box-shadow] outline-none focus-visible:ring-[3px] focus-visible:outline-1"
+      >
+        {children}
+      </ScrollAreaPrimitive.Viewport>
+      <ScrollBar />
+      <ScrollAreaPrimitive.Corner />
+    </ScrollAreaPrimitive.Root>
+  );
+}
+
+function ScrollBar({
+  className,
+  orientation = "vertical",
+  ...props
+}: React.ComponentProps<typeof ScrollAreaPrimitive.ScrollAreaScrollbar>) {
+  return (
+    <ScrollAreaPrimitive.ScrollAreaScrollbar
+      data-slot="scroll-area-scrollbar"
+      orientation={orientation}
+      className={cn(
+        "flex touch-none p-px transition-colors select-none",
+        orientation === "vertical" &&
+          "h-full w-2.5 border-l border-l-transparent",
+        orientation === "horizontal" &&
+          "h-2.5 flex-col border-t border-t-transparent",
+        className
+      )}
+      {...props}
+    >
+      <ScrollAreaPrimitive.ScrollAreaThumb
+        data-slot="scroll-area-thumb"
+        className="bg-border relative flex-1 rounded-full"
+      />
+    </ScrollAreaPrimitive.ScrollAreaScrollbar>
+  );
+}
+
+export { ScrollArea, ScrollBar };