refactor: migrate scripts from argparse to click, add YAML config support

- Replace argparse with click in all scripts (train, server, generate,
  preprocess, benchmark)
- Add --config YAML support to train.py with CLI flag override
- Add --dry-run mode to validate config before training
- Add type annotations throughout benchmark.py
- Unify docstring format across all commands
- Remove redundant deps httpx, requests, pyyaml, rich from pyproject.toml
- Net -346 lines while adding YAML config support

.gitignore

@@ -29,6 +29,7 @@
 !/LICENSE
 !/pyproject.toml
 !/README.md
+!/AGENTS.md
 # Allow extension modules (only source .py)
 !/astrai/extension/**/*.py