refactor(cli): split claude_bottle/cli.py into a package

One file per subcommand under claude_bottle/cli/, with shared constants
and the tty helper in _common.py and dispatch in __init__.py. The
public import (from claude_bottle.cli import main) is unchanged, so
the root cli.py entrypoint and the test suite see no surface change.

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

claude_bottle/cli/build.py

@@ -0,0 +1,15 @@
+"""build: build (or rebuild) the claude-bottle Docker image."""
+
+from __future__ import annotations
+
+import os
+
+from .. import docker as docker_mod
+from ._common import REPO_DIR
+
+
+def cmd_build(_argv: list[str]) -> int:
+    docker_mod.require_docker()
+    image = os.environ.get("CLAUDE_BOTTLE_IMAGE", "claude-bottle:latest")
+    docker_mod.build_image(image, REPO_DIR)
+    return 0