chore(backend): drop dead code left by the InfraService refactor

Remove symbols with no remaining consumer:

- `gateway_name` property on Docker/MacosInfraService — nothing uses it; the
  launch flow reads `gateway().name` off the Gateway service. (+ its docker test.)
- firecracker `infra_vm` EGRESS_PORT / SUPERVISE_PORT / GIT_HTTP_PORT — dead
  duplicates; launch.py uses supervisor.types / docker.egress / a local const.
- macOS `INFRA_DB_VOLUME` back-compat alias — unused since the DB-volume test
  moved to `ORCHESTRATOR_DB_VOLUME`.
- docker `infra.py`: the unused `ORCHESTRATOR_SOURCE_HASH_LABEL` import and the
  `__all__` re-exports of the orchestrator constants (consumers import them from
  `docker.orchestrator`, not `docker.infra`).
- macOS `infra.py`: the unused `GatewayError` import + re-export.

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

bot_bottle/backend/docker/infra.py

@@ -32,7 +32,6 @@ from .orchestrator import (
     ORCHESTRATOR_LABEL,
     ORCHESTRATOR_NAME,
     ORCHESTRATOR_NETWORK,
-    ORCHESTRATOR_SOURCE_HASH_LABEL,
 )
 from ...paths import bot_bottle_root
 from ...gateway import (
@@ -86,12 +85,6 @@ class DockerInfraService(InfraService):
         self._orchestrator_label = orchestrator_label
         self._gateway_name = gateway_name
 
-    @property
-    def gateway_name(self) -> str:
-        """The gateway container — the address the launch flow attributes agents
-        against (gateway IP, git-gate provisioning transport, CA fetch)."""
-        return self._gateway_name
-
     def orchestrator(self) -> DockerOrchestrator:
         """The control-plane service. Cheap to reconstruct — `ensure_built`
         builds its image, `ensure_running` brings it up, and the launch flow
@@ -155,8 +148,5 @@ class DockerInfraService(InfraService):
 __all__ = [
     "DockerInfraService",
     "ORCHESTRATOR_NAME",
-    "ORCHESTRATOR_NETWORK",
-    "ORCHESTRATOR_IMAGE",
-    "ORCHESTRATOR_SOURCE_HASH_LABEL",
     "INFRA_NAME",
 ]