refactor(backend): pass Bottle to provisioners instead of target string

Closes #178.

The backend provision functions now receive a Bottle handle with
exec / cp_in methods instead of a raw target string. Provisioner
modules use bottle.exec and bottle.cp_in in place of inlined
subprocess.run(["docker", "exec"/"cp", ...]) and direct
_smolvm.machine_cp / machine_exec calls. This decouples the
provisioners from backend-specific runtime primitives so future
refactors (e.g. the supervise rework) can swap the bottle's exec
implementation without touching every provisioner.

Each launch.py constructs the Bottle handle before calling
provision so it can be passed in; provision_prompt's return value
is wired back onto the bottle's prompt path attribute after the
fact.

bot_bottle/backend/docker/provision/skills.py

@@ -9,54 +9,36 @@ a partial container."""
 from __future__ import annotations
 
 import os
-import subprocess
 
 from ....log import die, info
 from ...util import host_skill_dir
+from ... import Bottle
 from ..bottle_plan import DockerBottlePlan
 
 
-def provision_skills(plan: DockerBottlePlan, target: str) -> None:
+def provision_skills(plan: DockerBottlePlan, bottle: Bottle) -> None:
     """Copy each of the agent's named skills from the host's
     ~/.claude/skills/<name>/ into the container's equivalent path.
     For each skill: ensure parent dir, wipe any prior copy, then
-    `docker cp <host>/. <container>:<dst>/` so the contents are
+    `cp_in <host>/. <container>:<dst>/` so the contents are
     copied into a freshly-created destination dir. No-op when the
     agent has no skills."""
     agent = plan.spec.manifest.agents[plan.spec.agent_name]
     if not agent.skills:
         return
 
-    container = target
     container_home = os.environ.get("BOT_BOTTLE_CONTAINER_HOME", "/home/node")
     skills_dir = os.environ.get(
         "BOT_BOTTLE_CONTAINER_SKILLS_DIR", f"{container_home}/.claude/skills"
     )
 
-    subprocess.run(
-        ["docker", "exec", container, "mkdir", "-p", skills_dir],
-        stdout=subprocess.DEVNULL,
-        check=True,
-    )
+    bottle.exec(f"mkdir -p {skills_dir}", user="node")
 
     for n in agent.skills:
         src = host_skill_dir(n)
         if not os.path.isdir(src):
             die(f"skill '{n}' disappeared from host between validation and copy at {src}.")
         dst = f"{skills_dir}/{n}"
-        info(f"copying skill {n} into {container}:{dst}")
-        subprocess.run(
-            ["docker", "exec", container, "rm", "-rf", dst],
-            stdout=subprocess.DEVNULL,
-            check=True,
-        )
-        subprocess.run(
-            ["docker", "exec", container, "mkdir", "-p", dst],
-            stdout=subprocess.DEVNULL,
-            check=True,
-        )
-        subprocess.run(
-            ["docker", "cp", f"{src}/.", f"{container}:{dst}/"],
-            stdout=subprocess.DEVNULL,
-            check=True,
-        )
+        info(f"copying skill {n} into {bottle.name}:{dst}")
+        bottle.exec(f"rm -rf {dst} && mkdir -p {dst}", user="node")
+        bottle.cp_in(f"{src}/.", f"{dst}/")