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/firecracker/infra_vm.py

@@ -74,11 +74,6 @@ _ROOTFS_IMAGE = {"orchestrator": _ORCHESTRATOR_FC_IMAGE, "gateway": _GATEWAY_IMA
 _ROOTFS_SLACK_MIB = {"orchestrator": 8192, "gateway": 1024}
 
 ORCHESTRATOR_PORT = 8099
-# Gateway data-plane ports (agent-facing): egress proxy, supervise MCP,
-# git-http. Reached by agent VMs via the PREROUTING DNAT to the gateway VM.
-EGRESS_PORT = 9099
-SUPERVISE_PORT = 9100
-GIT_HTTP_PORT = 9420
 
 # The infra VMs make direct upstream connections (gateway egress, and buildah
 # during builds), and the kernel `ip=` cmdline sets no resolver. Public for