refactor: separate standalone and managed room configs

- veins → shunts rename
- add cfg/standalone/ and cfg/<room>/ structure
- remove old data/*.json (moved to cfg/<room>/data/)
- update build.py and ctrl scripts

artery/shunts/mercadopago/main.py

@@ -0,0 +1,40 @@
+"""MercadoPago (MOCK) Vein - FastAPI app."""
+
+from pathlib import Path
+from fastapi import FastAPI, Request
+from fastapi.responses import HTMLResponse
+from fastapi.templating import Jinja2Templates
+from fastapi.middleware.cors import CORSMiddleware
+from .api.routes import router
+from .core.config import settings
+
+app = FastAPI(
+    title="MercadoPago (MOCK)",
+    description="Mock MercadoPago API for testing - simulates payment processing",
+    version="0.1.0",
+)
+
+# Enable CORS for testing from backend
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],  # In production, specify exact origins
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Templates for configuration UI
+templates = Jinja2Templates(directory=Path(__file__).parent / "templates")
+
+@app.get("/", response_class=HTMLResponse)
+def index(request: Request):
+    """Mock configuration UI."""
+    return templates.TemplateResponse("index.html", {"request": request})
+
+# Include router at root (matches real MercadoPago API structure)
+app.include_router(router)
+
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run(app, host="0.0.0.0", port=settings.api_port)