refactor(firecracker): orchestrator under the Orchestrator service ABC

Pull the control plane's host-side logic out of `infra_vm` into
`FirecrackerOrchestrator` (backend/firecracker/orchestrator.py): booting the
orchestrator microVM on its link with the persistent registry volume (/dev/vdb),
seeding the host-canonical signing key over SSH, waiting for /health, and the
buildah SSH target. `url()` == `gateway_url()` (the gateway resolves the
orchestrator by guest IP via bb_orch). This completes the trio — docker, macOS,
firecracker — behind both the Gateway and Orchestrator ABCs.

`infra_vm` stays the pair coordinator + shared substrate: `ensure_running` now
mints nothing itself — it constructs both services (lazy import to break the
cycle), calls `orchestrator.ensure_running()` first, then
`gateway.connect_to_orchestrator(orch.gateway_url(), orch.mint_gateway_token())`.
The plane-agnostic boot primitives graduate to public API (`_boot_vm`/
`_push_secret` -> `boot_vm`/`push_secret`) now that they're consumed only across
modules; `InfraVm` loses its `orchestrator_url` (moved to the service) and
`InfraEndpoint.orchestrator` is now the `FirecrackerOrchestrator` service.

Container-lifecycle tests split into test_firecracker_orchestrator; the infra_vm
tests keep the substrate + pair-coordinator coverage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/backend/firecracker/gateway.py

@@ -9,7 +9,7 @@ only the token the host hands it via `connect_to_orchestrator`.
 
 What deliberately stays in `infra_vm` (not moved here): the plane-agnostic VM
 substrate the orchestrator VM shares — booting a VM from the shared rootfs
-(`_boot_vm`), the stable SSH keypair, the secret-push retry loop, and the PID
+(`boot_vm`), the stable SSH keypair, the secret-push retry loop, and the PID
 lifecycle — plus the pair coordinator (`ensure_running`: orchestrator-first
 health gate, singleton lock, adoption/version marker). The guest-side gateway
 daemon startup lives in the shared `bb_role=gateway` init branch baked into the
@@ -96,12 +96,12 @@ class FirecrackerGateway(Gateway):
             )
         # Boot on the gateway link from the shared rootfs (bb_role=gateway), then
         # push the token the init waits for before starting the data plane.
-        vm = infra_vm._boot_vm(
+        vm = infra_vm.boot_vm(
             name=GATEWAY_NAME, slot=netpool.gw_slot(), run_dir=infra_vm._gw_dir(),
             role="gateway", mem_mib=_GW_MEM_MIB,
             extra_boot_args=f"bb_orch={orchestrator_guest_ip}",
         )
-        infra_vm._push_secret(
+        infra_vm.push_secret(
             vm, self._gateway_token, _GUEST_GATEWAY_JWT_PATH,
             "the gateway JWT to the gateway VM (its data plane will not start)",
         )