feat: add SPA, serve at /app/, update Dockerfile and README

- React + TanStack Router + shadcn/ui SPA under spa/
- serve spa/dist at /app/ with index.html fallback for client routing
- Dockerfile: node build stage for SPA, copy dist into runtime image
- README: document SPA, CORS_ORIGINS env var, architecture entry
- vite base set to /app/, manifest.json paths fixed

spa/src/components/star-rating.tsx

@@ -0,0 +1,34 @@
+import { Star } from "lucide-react"
+import { cn } from "@/lib/utils"
+
+type StarRatingProps = {
+  value: number
+  onChange: (value: number) => void
+  size?: "sm" | "md" | "lg"
+}
+
+const sizes = { sm: "size-5", md: "size-8", lg: "size-10" }
+
+export function StarRating({ value, onChange, size = "lg" }: StarRatingProps) {
+  return (
+    <div className="flex gap-1">
+      {[1, 2, 3, 4, 5].map((star) => (
+        <button
+          key={star}
+          type="button"
+          onClick={() => onChange(star)}
+          className="transition-transform active:scale-90"
+        >
+          <Star
+            className={cn(
+              sizes[size],
+              star <= value
+                ? "fill-amber-500 text-amber-500 aero-star-filled"
+                : "text-muted-foreground/30",
+            )}
+          />
+        </button>
+      ))}
+    </div>
+  )
+}