refactor(docker): inline skills_copy_into into provision_skills

The copy logic was Docker-specific (docker exec mkdir / rm -rf,
docker cp); it had no reason to live in a top-level skills module.
Pull the body into DockerBottleBackend.provision_skills.

skills.py keeps the host-side discovery + validation
(host_skill_dir, host_skill_exists, require_host_skill,
skills_validate_all). The orphaned CONTAINER_HOME /
CONTAINER_SKILLS_DIR constants and the now-unused subprocess + info
imports are removed.

claude_bottle/backend/docker/backend.py

@@ -292,12 +292,48 @@ class DockerBottleBackend(BottleBackend):
     def provision_skills(self, plan: BottlePlan, target: str) -> None:
         """Copy each of the agent's named skills from the host's
         ~/.claude/skills/<name>/ into the container's equivalent path.
-        No-op when the agent has no skills."""
+        For each skill: ensure parent dir, wipe any prior copy, then
+        `docker cp <host>/. <container>:<dst>/` so the contents are
+        copied into a freshly-created destination dir. No-op when the
+        agent has no skills."""
         assert isinstance(plan, DockerBottlePlan)
         agent = plan.spec.manifest.agents[plan.spec.agent_name]
         if not agent.skills:
             return
-        skills_mod.skills_copy_into(target, list(agent.skills))
+
+        container = target
+        container_home = os.environ.get("CLAUDE_BOTTLE_CONTAINER_HOME", "/home/node")
+        skills_dir = os.environ.get(
+            "CLAUDE_BOTTLE_CONTAINER_SKILLS_DIR", f"{container_home}/.claude/skills"
+        )
+
+        subprocess.run(
+            ["docker", "exec", container, "mkdir", "-p", skills_dir],
+            stdout=subprocess.DEVNULL,
+            check=True,
+        )
+
+        for n in agent.skills:
+            src = skills_mod.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,
+            )
 
     def provision_ssh(self, plan: BottlePlan, target: str) -> None:
         """If the bottle has SSH entries, set up the in-container