Both docker and smolmachines resolve_plan.py duplicated: slug minting,
metadata writing, agent state dir setup, git gate / egress / supervise
preparation, env_vars merge, and manifest dockerfile path resolution.
These are now consolidated in bot_bottle/backend/resolve_common.py.
Each backend's resolve_plan retains only its own logic (container name
resolution + env-file for docker; subnet allocation + guest_env build
for smolmachines).
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.