Add percent-based order sizing

[nozprod]

Fixes #9.

Summary

• Adds optional qty_percent support so alerts can size an order from a percentage of available quote-currency balance instead of a fixed qty.
• Keeps the existing fixed qty behavior unchanged when qty_percent is not provided.
• Applies the sizing path to Bybit and Binance Futures order placement.
• Fixes the Binance Futures config-key mismatch and webhook routing indentation so that exchange path can actually run.
• Documents the new alert fields in the README.

Verification

• PYTHONPYCACHEPREFIX=/private/tmp/pycache python3 -m py_compile app.py binanceFutures.py
• git diff --check

Bounty / payout

This is a submission for the paid crypto bounty on #9. If accepted, payout can be sent as ERC20/USDC to: 0x3a2719e116c9C69a2514F3F7287b4AAAb13B9726.

Disclosure: this PR was prepared with AI assistance and reviewed before submission.