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/.env.example

@@ -0,0 +1,16 @@
+# MercadoPago (MOCK) Vein Configuration
+API_PORT=8006
+
+# Mock data settings
+MOCK_DATA_PATH=./mock_data
+
+# Mock behavior
+ENABLE_RANDOM_DELAYS=true
+MIN_DELAY_MS=200
+MAX_DELAY_MS=800
+
+# Simulate errors
+ERROR_RATE=0.0  # 0.0 to 1.0 (0% to 100%)
+
+# Default payment status for testing
+DEFAULT_PAYMENT_STATUS=approved  # approved, pending, rejected