chore: comment out workspace + capability_apply, fix circular imports

The recent refactor partially removed workspace planning and
capability-apply logic. This commit finishes the cleanup so the
test suite imports cleanly:

- Comment out workspace_plan field/property on BottlePlan and the
  provision_workspace dispatch.
- Comment out workspace usages in docker.util (build_image_with_cwd),
  smolmachines.provision.workspace, agent_provider.provision_git,
  smolmachines.backend.
- Comment out capability_apply imports in cli.start and cli.supervise;
  add a local CapabilityApplyError placeholder so the supervise CLI
  module still imports.
- Break the bottle_state → backend.docker → backend circular import
  by lazy-loading docker_mod inside bottle_identity, and by moving the
  resolve_common import inside BottleBackend.prepare.
- Delete tests for workspace and capability_apply (unit + integration).
- Update test fixtures to drop removed kwargs (container_name_pinned,
  derived_image, env_file, workspace_plan, agent_image_ref) from
  DockerBottlePlan / SmolmachinesBottlePlan constructors.
- Delete the obsolete test_smolmachines_prepare.py (tested the old
  resolve_plan signature; the shared prepare flow now lives in
  BottleBackend.prepare).
- Adjust test_supervise.py for the new Supervise.prepare signature
  (dockerfile_content arg removed).

925 → 897 tests, all passing.

bot_bottle/bottle_state.py

@@ -38,7 +38,6 @@ from pathlib import Path
 from typing import cast
 
 from . import supervise as _supervise
-from .backend.docker import util as docker_mod
 
 
 # Directory layout: ~/.bot-bottle/state/<identity>/...
@@ -82,6 +81,7 @@ def bottle_identity(agent_name: str) -> str:
     To continue an existing bottle's state, use the recorded
     identity from BottleMetadata via `cli.py resume <identity>`,
     not this function."""
+    from .backend.docker import util as docker_mod
     slug = docker_mod.slugify(agent_name)
     suffix = "".join(secrets.choice(_SUFFIX_ALPHABET) for _ in range(_RANDOM_SUFFIX_LEN))
     return f"{slug}-{suffix}"