refactor(orchestrator): rename Sidecar -> Gateway for the consolidated data plane

Retire "sidecar" for the consolidated per-host path (PRD 0070 naming
decision): the orchestrator is the umbrella/control plane, and the
egress/git/supervise data-plane unit it runs is the "gateway".

- git mv sidecar.py -> gateway.py and the two integration + one unit test
  files; DockerSidecar->DockerGateway, Sidecar->Gateway,
  SidecarError->GatewayError, SIDECAR_*->GATEWAY_*, ensure_sidecar->
  ensure_gateway, sidecar_status->gateway_status, container name
  bot-bottle-orch-sidecar->bot-bottle-orch-gateway.
- Prose rename across broker/registry/egress/policy_resolver + PRD 0070.
- Preserved: the image name bot-bottle-sidecars, the
  BOT_BOTTLE_SIDECAR_IMAGE env var, Dockerfile.sidecars, and PRD 0069's
  own stage-name cross-references (that doc still uses "sidecar").

No behavior change. Full unit suite green (1679 tests; the 13
test_sidecar_init /bin/sleep errors are pre-existing NixOS-local noise).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/orchestrator/__init__.py

@@ -1,6 +1,6 @@
 """Per-host orchestrator service (PRD 0070).
 
-A single persistent per-host service that will run the sidecar functions
+A single persistent per-host service that will run the gateway functions
 (egress / git-gate / supervise), coordinate with the console, and broker
 agent launches. This package is being built bottom-up, starting with the
 backend-neutral "consolidation core" that needs no VM packaging:
@@ -10,15 +10,15 @@ backend-neutral "consolidation core" that needs no VM packaging:
   * `broker`        — the signed, structured launch-request contract + a
                       `LaunchBroker` (stub for the harness) that verifies
                       provenance before acting.
-  * `sidecar`       — the consolidated per-host sidecar: a `Sidecar`
+  * `gateway`       — the consolidated per-host gateway: a `Gateway`
                       lifecycle contract (idempotent singleton) + a
-                      `DockerSidecar` impl. One sidecar shared by all
+                      `DockerGateway` impl. One gateway shared by all
                       bottles instead of one per bottle.
   * `service`       — the `Orchestrator`: owns the registry, brokers the
                       launch lifecycle (launch/teardown), manages the
-                      shared sidecar, attributes.
+                      shared gateway, attributes.
   * `control_plane` — the HTTP control-plane RPC (launch / teardown /
-                      list / attribute / sidecar / health).
+                      list / attribute / gateway / health).
 
 The actual backend-native launch (a real docker/firecracker broker) and
 the egress/git/supervise data plane land in later slices once this core is
@@ -38,7 +38,7 @@ from .broker import (
     verify_request,
 )
 from .docker_broker import DockerBroker, DockerBrokerError
-from .sidecar import DockerSidecar, Sidecar, SidecarError
+from .gateway import DockerGateway, Gateway, GatewayError
 from .service import Orchestrator
 from .control_plane import ControlPlaneServer, dispatch, make_server
 
@@ -52,9 +52,9 @@ __all__ = [
     "StubBroker",
     "DockerBroker",
     "DockerBrokerError",
-    "Sidecar",
-    "DockerSidecar",
-    "SidecarError",
+    "Gateway",
+    "DockerGateway",
+    "GatewayError",
     "sign_request",
     "verify_request",
     "Orchestrator",