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/review-card.tsx

@@ -0,0 +1,44 @@
+import { Link } from "@tanstack/react-router"
+import { StarDisplay } from "@/components/star-display"
+import { Card, CardContent } from "@/components/ui/card"
+import { posterUrl } from "@/lib/api/client"
+import type { MovieDto, ReviewDto } from "@/lib/api/common"
+
+type ReviewCardProps = {
+  movie: MovieDto
+  review: ReviewDto
+  userName?: string
+  userId?: string
+}
+
+export function ReviewCard({ movie, review, userName, userId }: ReviewCardProps) {
+  return (
+    <Card size="sm">
+      <CardContent className="flex gap-3">
+        <Link to="/movies/$id" params={{ id: movie.id }} className="h-[84px] w-14 flex-shrink-0 overflow-hidden rounded-lg bg-muted">
+          {movie.poster_path && <img src={posterUrl(movie.poster_path)} alt="" className="size-full object-cover" />}
+        </Link>
+        <div className="min-w-0 flex-1">
+          {userName && (
+            <div className="flex items-center gap-1 text-xs text-muted-foreground">
+              {userId ? (
+                <Link to="/users/$id" params={{ id: userId }} className="relative z-10 font-semibold text-primary">
+                  {userName}
+                </Link>
+              ) : (
+                <span>{userName}</span>
+              )}
+              <span>·</span>
+              <span>{review.watched_at.slice(0, 10)}</span>
+            </div>
+          )}
+          <Link to="/movies/$id" params={{ id: movie.id }} className="font-semibold hover:underline">
+            {movie.title}
+          </Link>
+          <StarDisplay rating={review.rating} />
+          {review.comment && <p className="mt-1 line-clamp-2 text-xs text-muted-foreground">{review.comment}</p>}
+        </div>
+      </CardContent>
+    </Card>
+  )
+}