refactor(platform): rename claude_bottle/bottles -> claude_bottle/platform

'bottles' was the package name when it held a single Bottle Protocol;
since we added BottlePlatform / BottlePlan / BottleCleanupPlan and
made it the home of platform dispatch, 'platform' describes the
package better. The 'bottle' concept (and the manifest field) stays.

CLI imports update from ..bottles to ..platform; internal relative
imports inside the package survive the rename unchanged. Git
detected all 7 file renames.

claude_bottle/platform/docker/util.py

@@ -0,0 +1,108 @@
+"""Docker host-side primitives used by DockerBottlePlatform: probing
+for docker on PATH, slugifying agent names, checking image/container
+existence, and building images."""
+
+from __future__ import annotations
+
+import re
+import shutil
+import subprocess
+from typing import Iterable
+
+from ...log import die, info
+
+
+def runsc_available() -> bool:
+    """Return True if the Docker daemon has the gVisor (`runsc`) runtime
+    registered. Called once per prepare; the result lives on the plan."""
+    r = subprocess.run(
+        ["docker", "info", "--format", "{{json .Runtimes}}"],
+        capture_output=True,
+        text=True,
+    )
+    return r.returncode == 0 and "runsc" in r.stdout
+
+
+def require_docker() -> None:
+    """Fail with an install pointer if `docker` is not on PATH."""
+    if shutil.which("docker") is None:
+        info("Docker is required but was not found on PATH.")
+        info("macOS:  install Docker Desktop  https://docs.docker.com/desktop/install/mac-install/")
+        info("Linux:  install Docker Engine   https://docs.docker.com/engine/install/")
+        die("docker not found")
+
+
+def image_exists(ref: str) -> bool:
+    return _silent_run(["docker", "image", "inspect", ref]) == 0
+
+
+def container_exists(name: str) -> bool:
+    """Returns True if a container (running or stopped) with the given
+    name exists. Uses `docker ps -a -q -f name=^<name>$` so substring
+    matches don't false-positive."""
+    result = subprocess.run(
+        ["docker", "ps", "-a", "-q", "-f", f"name=^{name}$"],
+        capture_output=True,
+        text=True,
+    )
+    return bool(result.stdout.strip())
+
+
+_SLUG_RE = re.compile(r"[^a-z0-9]+")
+
+
+def slugify(name: str) -> str:
+    """Lowercase, non-alnum runs → '-', trimmed. Dies on empty result."""
+    if not name:
+        die("slugify: missing name")
+    slug = _SLUG_RE.sub("-", name.lower()).strip("-")
+    if not slug:
+        die(f"name '{name}' produced an empty slug; use alphanumeric characters")
+    return slug
+
+
+def build_image(ref: str, context: str) -> None:
+    """Invokes `docker build` every call. Layer cache makes no-change
+    rebuilds cheap; running every time means Dockerfile edits land
+    without manual `docker rmi`."""
+    info(f"building image {ref} from {context} (layer cache keeps repeat builds fast)")
+    subprocess.run(["docker", "build", "-t", ref, context], check=True)
+
+
+_TRUST_DIALOG_NODE_SCRIPT = (
+    'const fs=require("fs"),p=process.env.HOME+"/.claude.json",'
+    'c=JSON.parse(fs.readFileSync(p,"utf8"));'
+    'c.projects=c.projects||{};'
+    'c.projects[process.env.HOME+"/workspace"]={hasTrustDialogAccepted:true};'
+    'fs.writeFileSync(p,JSON.stringify(c,null,2));'
+)
+
+
+def build_image_with_cwd(derived: str, base: str, cwd: str) -> None:
+    """Build a thin derived image that copies <cwd> into
+    /home/node/workspace and adds a trust-dialog entry for it."""
+    import os
+
+    if not os.path.isdir(cwd):
+        die(f"cwd not found at {cwd}")
+    info(f"building image {derived} from {base} with {cwd} -> /home/node/workspace")
+    dockerfile = (
+        f"FROM {base}\n"
+        f"COPY --chown=node:node . /home/node/workspace\n"
+        f"RUN node -e '{_TRUST_DIALOG_NODE_SCRIPT}'\n"
+        f"WORKDIR /home/node/workspace\n"
+    )
+    subprocess.run(
+        ["docker", "build", "-t", derived, "-f", "-", cwd],
+        input=dockerfile,
+        text=True,
+        check=True,
+    )
+
+
+def _silent_run(cmd: Iterable[str]) -> int:
+    return subprocess.run(
+        list(cmd),
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.DEVNULL,
+    ).returncode