refactor(backend): move git-gate provisioning to a neutral module

`backend/docker/gateway_provision.py` had no docker-specific code left once
`DockerGatewayTransport` moved out — `provision_git_gate` / `deprovision_git_gate`
drive any `GatewayTransport`, and the guest-side paths they write
(`/git-gate/creds/<id>`, `/git/<id>`, `/etc/git-gate/...`) are identical inside
every backend's gateway. Yet the neutral `backend/consolidated_util.py` reached
into the docker package to import them.

Move it to `backend/gateway_provision.py`, a sibling of its only importer. The
gateway *package* can't host it (git_gate already imports gateway.git_gate,
so gateway importing git_gate would cycle), but the backend layer uses git_gate
freely. Docstrings + the git_gate/service.py pointer updated.

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

bot_bottle/backend/consolidated_util.py

@@ -14,7 +14,7 @@ from ..git_gate import GitGatePlan
 from ..orchestrator.client import OrchestratorClient, RegisteredBottle
 from ..orchestrator.registration import registration_inputs
 from ..orchestrator.store.secret_store import new_env_var_secret
-from .docker.gateway_provision import GatewayTransport, deprovision_git_gate, provision_git_gate
+from .gateway_provision import GatewayTransport, deprovision_git_gate, provision_git_gate
 
 
 def provision_bottle(

bot_bottle/backend/docker/gateway_transport.py

@@ -2,7 +2,7 @@
 
 How the launcher stages files + runs commands in the running gateway container:
 `docker exec` / `docker cp` over the docker socket. The backend-neutral
-provisioning logic that drives it lives in `gateway_provision`.
+provisioning logic that drives it lives in `backend.gateway_provision`.
 """
 
 from __future__ import annotations

bot_bottle/backend/firecracker/gateway_transport.py

@@ -4,7 +4,7 @@
 How the launcher stages files + runs commands in the running gateway: the
 docker exec/cp equivalents over SSH (dropbear + the stable infra key). The
 backend-neutral provisioning logic that drives it lives in
-`backend.docker.gateway_provision`.
+`backend.gateway_provision`.
 """
 
 from __future__ import annotations

bot_bottle/backend/gateway_provision.py

@@ -1,12 +1,14 @@
 """Provision one bottle's git-gate state into the running shared gateway
-(PRD 0070, docker slice).
+(PRD 0070). Backend-neutral: it drives any `GatewayTransport` (docker/apple
+exec+cp, firecracker SSH), and the guest-side paths it writes are identical
+inside every backend's gateway because they all run the same gateway image.
 
 The consolidated gateway serves every bottle's repos under `/git/<bottle_id>/`
 with per-repo credentials under `/git-gate/creds/<bottle_id>/`. When a bottle
 is registered the launcher must place *its* deploy keys + known_hosts into
 that per-bottle creds dir and init its bare repos there — so this copies the
-credential files into the live gateway container and runs the (namespaced,
-init-only) provisioning script produced by `git_gate_render_provision`.
+credential files into the live gateway and runs the (namespaced, init-only)
+provisioning script produced by `git_gate_render_provision`.
 
 Isolating each bottle's creds dir + repo root by id is what keeps one
 bottle's push credentials out of another's repos on the shared gateway.
@@ -16,8 +18,8 @@ from __future__ import annotations
 
 import re
 
-from ...git_gate import GitGatePlan, git_gate_render_provision
-from ...gateway import GatewayProvisionError, GatewayTransport
+from ..git_gate import GitGatePlan, git_gate_render_provision
+from ..gateway import GatewayProvisionError, GatewayTransport
 
 # bottle ids index the gateway's per-bottle repo + creds dirs; they land in
 # exec/cp path arguments, so validate before any path is built (a traversal

bot_bottle/backend/macos_container/gateway_transport.py

@@ -2,7 +2,7 @@
 
 How the launcher stages files + runs commands in the running gateway container:
 the `container` CLI's exec/cp equivalents. The backend-neutral provisioning
-logic that drives it lives in `backend.docker.gateway_provision`; Docker uses
+logic that drives it lives in `backend.gateway_provision`; Docker uses
 `docker exec`/`docker cp` and Firecracker uses SSH.
 """
 

bot_bottle/git_gate/service.py

@@ -60,7 +60,7 @@ class GitGate:
         # `sh`, so the script needs the x bit. The gateway copy does not
         # necessarily preserve this mode (`docker cp` does, the Apple `container
         # cp` does not), so provisioning re-applies +x on the gateway side — see
-        # backend/docker/gateway_provision.py.
+        # backend/gateway_provision.py.
         access_hook.chmod(0o700)
         upstreams_with_files: list[GitGateUpstream] = []
         for u in upstreams: