refactor: move bottle_state.py to top-level bot_bottle package

Both docker and smolmachines backends use bottle state helpers.
Moving to bot_bottle/ makes the sharing explicit and removes the
cross-backend dependency (smolmachines importing from ..docker).

All callers updated: docker backend, smolmachines backend, cli
modules, and tests.

bot_bottle/cli/resume.py

@@ -18,7 +18,7 @@ from __future__ import annotations
 import argparse
 
 from ..backend import BottleSpec
-from ..backend.docker.bottle_state import read_metadata
+from ..bottle_state import read_metadata
 from ..log import die
 from ..manifest import Manifest
 from ._common import PROG, USER_CWD