Add Binance exchange support for spot/perp/options

- Binance spot orders (POST /api/v3/order) with HMAC-SHA256 signing
- Binance futures orders (POST /fapi/v1/order)
- Binance options orders (POST /eapi/v1/order)
- Binance balance, positions, open orders, cancel
- Global --exchange flag: auto|hyperliquid|binance
- Auto mode: Hyperliquid for spot/perp, Binance for options
- Options on Hyperliquid returns clear error (HIP-4 not ready)
- Binance order IDs: binance_spot:SYMBOL:OID, binance_futures:SYMBOL:OID
- Config: binance_api_key, binance_api_secret in [api_keys]
- Zero clippy warnings

Author: Michael Yuan

Cargo.toml

@@ -26,3 +26,5 @@ ethers = { version = "2", default-features = false, features = ["rustls", "eip71
 urlencoding = "2"
 regex = "1"
 openssl = { version = "0.10", features = ["vendored"] }
+hmac = "0.12"
+sha2 = "0.10"

config.toml.default

@@ -32,3 +32,8 @@ testnet = false
 # NewsAPI key — stock news (optional, not currently used)
 # Free at https://newsapi.org/
 # newsapi_key = "..."
+
+# Binance API credentials — enables spot/perp/options trading on Binance
+# Sign up at https://www.binance.com/
+# binance_api_key = "..."
+# binance_api_secret = "..."