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/util.py

@@ -258,8 +258,8 @@ def build_committed_rootfs_dir(tar_path: Path) -> Path:
 
 def inject_guest_boot(rootfs: Path, init_script: str | None = None) -> None:
     """Drop the static dropbear and the PID-1 init into the rootfs.
-    `init_script` defaults to the SSH-only agent init; the infra VM
-    passes its own (control plane + gateway) init.
+    `init_script` defaults to the SSH-only agent init; each infra VM
+    passes its own per-plane init (orchestrator or gateway).
 
     A committed snapshot is guest-controlled, so `bb-dropbear`/`bb-init`
     may already exist as symlinks aimed at a host file (e.g. bb-init ->