feat: harden trading SDK examples

examples/shared_infrastructure/README.md

@@ -0,0 +1,13 @@
+# Shared Infrastructure
+
+[中文](README_CN.md)
+
+Demonstrates sharing one `TradingInfrastructure` across multiple wallet-specific `TradingClient` values. This reduces connection, memory, and initialization overhead in multi-wallet services.
+
+Replace the RPC, SWQoS credentials, and all wallet placeholders in `src/main.rs`. The example initializes clients and prints sharing information; it does not submit a trade.
+
+```bash
+cargo run --package shared_infrastructure
+```
+
+Only share infrastructure when wallets use the same RPC, commitment, and submission routes. Keep wallet signing and position state isolated.