feat(fc2c-i): showcase random-sample service and endpoint

backend/app/api/showcase.py

@@ -0,0 +1,23 @@
+"""Showcase API: scalable random sample of images."""
+
+from quart import Blueprint, jsonify, request
+
+from ..extensions import get_session
+from ..services.showcase_service import ShowcaseService
+
+showcase_bp = Blueprint("showcase", __name__, url_prefix="/api/showcase")
+
+
+@showcase_bp.route("", methods=["GET"])
+async def random_showcase():
+    try:
+        limit = int(request.args.get("limit", "60"))
+    except ValueError:
+        return jsonify({"error": "limit must be an integer"}), 400
+    async with get_session() as session:
+        svc = ShowcaseService(session)
+        try:
+            images = await svc.random_sample(limit=limit)
+        except ValueError as exc:
+            return jsonify({"error": str(exc)}), 400
+    return jsonify({"images": images})