chore: release v3.0.0

- Bump version to 3.0.0 in pyproject.toml
- Update README with What's New section and new command examples
  (--window for tickers, --dry-run for catlog)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "coinhunter"
-version = "2.1.1"
+version = "3.0.0"
 description = "Binance-first trading CLI for balances, market data, opportunity scanning, and execution."
 readme = "README.md"
 license = {text = "MIT"}