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/breadcrumb.tsx

@@ -0,0 +1,109 @@
+import * as React from "react";
+import { Slot } from "@radix-ui/react-slot";
+import { ChevronRight, MoreHorizontal } from "lucide-react";
+
+import { cn } from "@/lib/utils";
+
+function Breadcrumb({ ...props }: React.ComponentProps<"nav">) {
+  return <nav aria-label="breadcrumb" data-slot="breadcrumb" {...props} />;
+}
+
+function BreadcrumbList({ className, ...props }: React.ComponentProps<"ol">) {
+  return (
+    <ol
+      data-slot="breadcrumb-list"
+      className={cn(
+        "text-muted-foreground flex flex-wrap items-center gap-1.5 text-sm break-words sm:gap-2.5",
+        className
+      )}
+      {...props}
+    />
+  );
+}
+
+function BreadcrumbItem({ className, ...props }: React.ComponentProps<"li">) {
+  return (
+    <li
+      data-slot="breadcrumb-item"
+      className={cn("inline-flex items-center gap-1.5", className)}
+      {...props}
+    />
+  );
+}
+
+function BreadcrumbLink({
+  asChild,
+  className,
+  ...props
+}: React.ComponentProps<"a"> & {
+  asChild?: boolean;
+}) {
+  const Comp = asChild ? Slot : "a";
+
+  return (
+    <Comp
+      data-slot="breadcrumb-link"
+      className={cn("hover:text-foreground transition-colors", className)}
+      {...props}
+    />
+  );
+}
+
+function BreadcrumbPage({ className, ...props }: React.ComponentProps<"span">) {
+  return (
+    <span
+      data-slot="breadcrumb-page"
+      role="link"
+      aria-disabled="true"
+      aria-current="page"
+      className={cn("text-foreground font-normal", className)}
+      {...props}
+    />
+  );
+}
+
+function BreadcrumbSeparator({
+  children,
+  className,
+  ...props
+}: React.ComponentProps<"li">) {
+  return (
+    <li
+      data-slot="breadcrumb-separator"
+      role="presentation"
+      aria-hidden="true"
+      className={cn("[&>svg]:size-3.5", className)}
+      {...props}
+    >
+      {children ?? <ChevronRight />}
+    </li>
+  );
+}
+
+function BreadcrumbEllipsis({
+  className,
+  ...props
+}: React.ComponentProps<"span">) {
+  return (
+    <span
+      data-slot="breadcrumb-ellipsis"
+      role="presentation"
+      aria-hidden="true"
+      className={cn("flex size-9 items-center justify-center", className)}
+      {...props}
+    >
+      <MoreHorizontal className="size-4" />
+      <span className="sr-only">More</span>
+    </span>
+  );
+}
+
+export {
+  Breadcrumb,
+  BreadcrumbList,
+  BreadcrumbItem,
+  BreadcrumbLink,
+  BreadcrumbPage,
+  BreadcrumbSeparator,
+  BreadcrumbEllipsis,
+};