refactor(backend): generic setup/status; drop firecracker-only CLI

Add abstract `setup()`/`status()` classmethods to BottleBackend (same
per-host, no-instance shape as is_available) so host provisioning is
part of the backend contract, not a per-backend command. Replace the
`./cli.py firecracker {setup,status}` command with a generic
`./cli.py backend {setup,status} [--backend=NAME]` that resolves a
backend (flag / $BOT_BOTTLE_BACKEND / host default) and dispatches —
swapping backends is just a different --backend.

Implementations:
- firecracker: moved out of cli/ into backend/firecracker/setup.py
  (network pool module/script + range-overlap check), unchanged output.
- docker: new backend/docker/setup.py — reports docker on PATH, daemon
  reachability, and gVisor runsc; setup notes no privileged pool is
  needed. Minimal placeholder; richer version tracked in #345.
- macos-container: new setup.py — container CLI + system-service checks.

Also retarget the launch-preflight / isolation-probe pointers to the new
command. New test_cli_backend covers dispatch + docker setup/status.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/backend/macos_container/setup.py

@@ -0,0 +1,69 @@
+"""Host setup + status for the macOS Apple Container backend.
+
+Like Docker, this backend needs no privileged network-pool provisioning
+— it wants Apple's `container` CLI installed and its system service
+running. `setup()` points at the install/`container system start` steps;
+`status()` reports readiness. Reached via
+`MacosContainerBottleBackend.setup` / `.status`, dispatched from the
+generic `./cli.py backend {setup,status}`.
+"""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+import sys
+
+from . import util as _container
+
+
+def _service_running() -> bool:
+    if shutil.which("container") is None:
+        return False
+    return subprocess.run(
+        ["container", "system", "status"],
+        stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, check=False,
+    ).returncode == 0
+
+
+def setup() -> int:
+    if not _container.is_macos():
+        sys.stderr.write("macos-container backend requires macOS.\n")
+        return 1
+    if shutil.which("container") is None:
+        sys.stderr.write("Apple Container is required but was not found on PATH.\n")
+        sys.stderr.write("Install: https://github.com/apple/container/releases\n")
+        return 1
+    if not _service_running():
+        sys.stderr.write(
+            "Apple Container is installed but its system service isn't "
+            "running. Start it with: container system start\n"
+        )
+        return 1
+    sys.stderr.write(
+        "macos-container backend: ready — no privileged host setup required.\n"
+    )
+    return 0
+
+
+def status() -> int:
+    ok = True
+    if _container.is_macos():
+        sys.stderr.write("host: macOS\n")
+    else:
+        sys.stderr.write("host: NOT macOS (backend unsupported here)\n")
+        ok = False
+    if shutil.which("container") is not None:
+        sys.stderr.write("container CLI on PATH: yes\n")
+    else:
+        sys.stderr.write("container CLI on PATH: NO\n")
+        ok = False
+    if ok:
+        sys.stderr.write(
+            f"container system service: {'running' if _service_running() else 'NOT running'}\n"
+        )
+        if not _service_running():
+            ok = False
+    if not ok:
+        sys.stderr.write("\nRun: ./cli.py backend setup --backend=macos-container\n")
+    return 0 if ok else 1