refactor: remove leftovers from the orchestrator/gateway consolidation

Sweep for vestiges of the old combined-plane model and the pre-split shared
rootfs. Two are load-bearing, the rest are stale docs/comments:

- Bug: macOS `enumerate_active` only excluded the gateway container from the
  agent list, so after the split the orchestrator container
  (`bot-bottle-mac-orchestrator`, also `bot-bottle-`-prefixed) was enumerated as
  a phantom agent. Exclude both infra containers; test covers it.
- Dead code: the gateway `bootstrap.py` still carried an `orchestrator` daemon
  spec + `_OPT_IN_DAEMONS` + a signing-key/JWT env branch, all for the old
  combined container where the gateway process could also run the control plane.
  No backend ever requests it now — removed; the key-stripping stays as
  defense-in-depth.

Stale-comment reframes: "the/single infra container" -> the orchestrator +
gateway pair (or the specific plane); "shared rootfs / bb_role init / one
published rootfs" -> the per-plane rootfs + `role_init`; the deleted
Dockerfile.infra references in Dockerfile.orchestrator/.gateway; and the macOS
"one infra container ... same address" docstring + its now-false
share-one-address test (the planes are distinct containers with distinct
addresses).

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

bot_bottle/backend/firecracker/firecracker_vm.py

@@ -69,8 +69,8 @@ def _boot_args(
     pub_b64 = base64.b64encode(pubkey.encode()).decode()
     args = f"{_BASE_BOOT_ARGS} {ip_arg} bb_pubkey={pub_b64}"
     # `extra` carries caller-supplied cmdline params the guest init reads
-    # (e.g. `bb_role=orchestrator|gateway` selecting which infra plane a
-    # shared-rootfs infra VM runs). Agent VMs pass nothing.
+    # (e.g. the gateway VM's `bb_orch=<orchestrator guest IP>`). Agent VMs pass
+    # nothing.
     return f"{args} {extra}".rstrip() if extra else args