`python -m bot_bottle.cli` failed with "is a package and cannot be
directly executed" — the package had a `if __name__ == "__main__"` block
in `__init__.py`, which never fires for a package and made the invocation
look supported when it wasn't. Add a real `__main__.py` and drop the dead
block.
Matters for `bb login`, whose docstring documents a `bb` entry point that
nothing installs; `-m` is the closest thing to it until there's a
console-script.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
