refactor(macos): one infra container (control plane + gateway), fixes shared-DB races

Adopts the firecracker infra-VM pattern for macOS: the orchestrator control
plane and the gateway data plane now run in a SINGLE Apple container instead of
two. Apple Containers are lightweight VMs with separate kernels, so the prior
two-container design had both guests writing one bot-bottle.db over virtiofs,
where fcntl locks are not coherent across kernels — concurrent writes (the
orchestrator's registry vs the gateway supervise daemon's queue) could corrupt
it. One container = one kernel = coherent locking.

The DB moves onto a container-only Apple volume (bot-bottle-mac-db), never
bind-mounted from the host, so no host process opens the live file either. The
host CLI already reaches registry + supervise state over the control-plane HTTP
surface (cli/supervise.py uses OrchestratorClient), exactly as firecracker's
VM-only DB requires.

Two simplifications fall out of the single container:
- No DNS dance: the control plane and gateway daemons reach each other over
  127.0.0.1, so the orchestrator-before-gateway ordering (a workaround for
  Apple having no container DNS) is gone, along with the moved-IP recreate
  logic it needed.
- Net -243 lines.

Mechanics: the infra container runs from the gateway image with the
control-plane source bind-mounted read-only (like the docker orchestrator, so a
code change needs no rebuild) and a small sh -c init that starts both processes
(mirrors firecracker's _infra_init). Also implements the macOS backend's
ensure_orchestrator() and adds it to discover_orchestrator_url, so operator
tools (supervise) can bring up / find the control plane on demand — previously
the macOS backend died with "no orchestrator control plane".

Verified end-to-end on real Apple Container 1.0.0: the single infra container
comes up healthy (one address for control plane + gateway), both processes run,
the DB is written on the container-only volume, host-side supervise works over
HTTP, and a registered agent gets 200 for an allowed host / 403 for a denied
one. 1824 unit tests pass with `container` absent (CI parity), pyright clean,
pylint 9.89.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bot_bottle/orchestrator/client.py

@@ -186,6 +186,13 @@ def discover_orchestrator_url(*, timeout: float = 2.0) -> str:
             f"http://{netpool.orch_slot().guest_ip}:{CONTROL_PLANE_PORT}")
     except Exception:  # noqa: BLE001 — backend optional / not firecracker
         pass
+    try:  # macOS: infra container control plane on its host-only address
+        from ..backend.macos_container.infra import probe_control_plane_url
+        url = probe_control_plane_url()
+        if url:
+            candidates.append(url)
+    except Exception:  # noqa: BLE001 — backend optional / not macOS
+        pass
     for url in candidates:
         if OrchestratorClient(url, timeout=timeout).health():
             return url