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/alert.tsx

@@ -0,0 +1,66 @@
+import * as React from "react";
+import { cva, type VariantProps } from "class-variance-authority";
+
+import { cn } from "@/lib/utils";
+
+const alertVariants = cva(
+  "relative w-full rounded-lg border px-4 py-3 text-sm grid has-[>svg]:grid-cols-[calc(var(--spacing)*4)_1fr] grid-cols-[0_1fr] has-[>svg]:gap-x-3 gap-y-0.5 items-start [&>svg]:size-4 [&>svg]:translate-y-0.5 [&>svg]:text-current",
+  {
+    variants: {
+      variant: {
+        default: "bg-card text-card-foreground",
+        destructive:
+          "text-destructive bg-card [&>svg]:text-current *:data-[slot=alert-description]:text-destructive/90",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+    },
+  }
+);
+
+function Alert({
+  className,
+  variant,
+  ...props
+}: React.ComponentProps<"div"> & VariantProps<typeof alertVariants>) {
+  return (
+    <div
+      data-slot="alert"
+      role="alert"
+      className={cn(alertVariants({ variant }), className)}
+      {...props}
+    />
+  );
+}
+
+function AlertTitle({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="alert-title"
+      className={cn(
+        "col-start-2 line-clamp-1 min-h-4 font-medium tracking-tight",
+        className
+      )}
+      {...props}
+    />
+  );
+}
+
+function AlertDescription({
+  className,
+  ...props
+}: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="alert-description"
+      className={cn(
+        "text-muted-foreground col-start-2 grid justify-items-start gap-1 text-sm [&_p]:leading-relaxed",
+        className
+      )}
+      {...props}
+    />
+  );
+}
+
+export { Alert, AlertTitle, AlertDescription };