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/kbd.tsx

@@ -0,0 +1,28 @@
+import { cn } from "@/lib/utils";
+
+function Kbd({ className, ...props }: React.ComponentProps<"kbd">) {
+  return (
+    <kbd
+      data-slot="kbd"
+      className={cn(
+        "bg-muted text-muted-foreground pointer-events-none inline-flex h-5 w-fit min-w-5 items-center justify-center gap-1 rounded-sm px-1 font-sans text-xs font-medium select-none",
+        "[&_svg:not([class*='size-'])]:size-3",
+        "[[data-slot=tooltip-content]_&]:bg-background/20 [[data-slot=tooltip-content]_&]:text-background dark:[[data-slot=tooltip-content]_&]:bg-background/10",
+        className
+      )}
+      {...props}
+    />
+  );
+}
+
+function KbdGroup({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <kbd
+      data-slot="kbd-group"
+      className={cn("inline-flex items-center gap-1", className)}
+      {...props}
+    />
+  );
+}
+
+export { Kbd, KbdGroup };