feat: add CLI aliases, flatten trade commands, and introduce --doc

- Add `coin` entry-point alias alongside `coinhunter`
- Add short aliases for all commands (e.g., a/acc, m, opp/o, b, s)
- Flatten `buy` and `sell` to top-level commands; remove `trade` parent
- Add `--doc` flag to print output schema and field descriptions per command
- Update README and tests
- Bump version to 2.1.0

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "coinhunter"
-version = "2.0.8"
+version = "2.1.0"
 description = "Binance-first trading CLI for balances, market data, opportunity scanning, and execution."
 readme = "README.md"
 license = {text = "MIT"}
@@ -27,6 +27,7 @@ dev = [
 
 [project.scripts]
 coinhunter = "coinhunter.cli:main"
+coin = "coinhunter.cli:main"
 
 [tool.setuptools]
 package-dir = {"" = "src"}