refactor(orchestrator): rename control_plane module to server

orchestrator/control_plane.py -> orchestrator/server.py. Within the
orchestrator package the "control_plane" filename stutters (the
orchestrator *is* the control plane), and `orchestrator.server` reads as
"the orchestrator's HTTP server", pairing with service.py (domain logic)
and matching gateway/supervisor/server.py.

Scope is the module name only. The class ControlPlaneServer, the
CONTROL_AUTH_HEADER constant, and the "control plane" architectural term
(CONTROL_PLANE_PORT, host_control_plane_token, control_plane_url, …) are
deliberately unchanged — that's the load-bearing control-plane/data-plane
distinction. Test file renamed to match; full unit suite green (2243).

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

bot_bottle/orchestrator/__init__.py

@@ -40,7 +40,7 @@ from .broker import (
 from .docker_broker import DockerBroker, DockerBrokerError
 from ..gateway import Gateway, GatewayError
 from .service import Orchestrator
-from .control_plane import ControlPlaneServer, dispatch, make_server
+from .server import ControlPlaneServer, dispatch, make_server
 
 __all__ = [
     "BottleRecord",