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.

tests/unit/test_supervise_cli.py

@@ -289,7 +289,7 @@ class TestCapabilityBlockSmolmachinesGuard(_FakeHomeMixin, unittest.TestCase):
         return supervise_cli.QueuedProposal(proposal=p, queue_dir=qdir)
 
     def _write_metadata(self, slug: str, compose_project: str) -> None:
-        from bot_bottle.backend.docker.bottle_state import BottleMetadata, write_metadata
+        from bot_bottle.bottle_state import BottleMetadata, write_metadata
         write_metadata(BottleMetadata(
             identity=slug,
             agent_name="myagent",