Add Binance Spot and KuCoin webhook support

[loganoe]

Summary

• Adds a Binance Spot exchange path using ccxt with BINANCE-SPOT config support.
• Adds KuCoin exchange support with API passphrase config.
• Routes exchange: "binance-spot" and exchange: "kucoin" webhook payloads for market/limit orders, order cancellation, and closing the current base-asset balance.
• Fixes the existing Binance dispatch path so Binance Futures is reachable outside the Bybit branch, and keeps futures using the configured uppercase BINANCE-FUTURES key.
• Updates README exchange docs and adds unit coverage for the new spot exchange bots.

Verification

• python3 -m py_compile app.py binanceFutures.py binanceSpot.py kucoin.py test_binance_spot.py test_kucoin.py
• /tmp/tvwb-venv/bin/python -m unittest test_binance_spot test_kucoin -v
• git diff --check

Closes #8
Closes #4

Bounty payout address if accepted: 0x7bE8796529f13882430ECeAB807712039E0dAfA2