refactor(openclaw): remove REST facade (port 8004), unify on WebSocket

Remove the redundant OpenClaw REST service (port 8004) since frontend
already uses WebSocket via Gateway (port 8765) → OpenClaw (port 18789).

Deleted:
- backend/apps/openclaw_service.py
- backend/api/openclaw.py
- backend/tests/test_openclaw_service_app.py
- backend/tests/test_service_clients.py
- shared/client/openclaw_client.py

Updated:
- backend/apps/__init__.py — remove openclaw_app exports
- backend/api/__init__.py — remove openclaw_router
- shared/client/__init__.py — remove OpenClawServiceClient
- backend/services/gateway_openclaw_handlers.py — update docstring
- start.sh — remove port 8004 service startup

Architecture:
- Before: Frontend → HTTP :8004 → subprocess openclaw CLI
- After: Frontend → WS :8765 → Gateway → WS :18789 → OpenClaw

Constraint: Frontend already uses WebSocket exclusively
Confidence: high
Scope-risk: low (frontend unchanged)

backend/apps/__init__.py

@@ -5,8 +5,6 @@ from .agent_service import app as agent_app
 from .agent_service import create_app as create_agent_app
 from .news_service import app as news_app
 from .news_service import create_app as create_news_app
-from .openclaw_service import app as openclaw_app
-from .openclaw_service import create_app as create_openclaw_app
 from .runtime_service import app as runtime_app
 from .runtime_service import create_app as create_runtime_app
 from .trading_service import app as trading_app
@@ -23,8 +21,6 @@ __all__ = [
     "create_agent_app",
     "news_app",
     "create_news_app",
-    "openclaw_app",
-    "create_openclaw_app",
     "runtime_app",
     "create_runtime_app",
     "trading_app",

backend/apps/openclaw_service.py

@@ -1,65 +0,0 @@
-# -*- coding: utf-8 -*-
-"""Read-only OpenClaw CLI FastAPI surface.
-
-COMPATIBILITY_SURFACE: deferred
-OWNER: runtime-team
-SEE: docs/legacy-inventory.md#openclaw-dual-integration
-
-This is the REST facade (port 8004) for OpenClaw integration.
-For the WebSocket gateway integration, see:
-  - backend/services/gateway_openclaw_handlers.py
-  - shared/client/openclaw_websocket_client.py
-
-Key differences:
-- REST facade: typed Pydantic models, request/response, polling
-- WebSocket: event-driven, real-time updates, bidirectional
-
-Decision needed: which surface becomes the long-term contract?
-"""
-
-from __future__ import annotations
-
-from fastapi import Depends, FastAPI
-
-from backend.api import openclaw_router
-from backend.apps.cors import add_cors_middleware
-from backend.api.openclaw import get_openclaw_cli_service
-
-
-def create_app() -> FastAPI:
-    """Create the OpenClaw service app."""
-    app = FastAPI(
-        title="大时代 OpenClaw Service",
-        description="Read-only OpenClaw CLI integration service surface",
-        version="0.1.0",
-    )
-
-    add_cors_middleware(app)
-
-    @app.get("/health")
-    async def health_check(
-        service=Depends(get_openclaw_cli_service),
-    ) -> dict[str, object]:
-        return service.health()
-
-    @app.get("/api/status")
-    async def api_status(
-        service=Depends(get_openclaw_cli_service),
-    ) -> dict[str, object]:
-        return {
-            "status": "operational",
-            "service": "openclaw-service",
-            "openclaw": service.health(),
-        }
-
-    app.include_router(openclaw_router)
-    return app
-
-
-app = create_app()
-
-
-if __name__ == "__main__":
-    import uvicorn
-
-    uvicorn.run(app, host="0.0.0.0", port=8004)