feat(standalone): 新增单机模式，KILOSTAR_MODE=standalone 时去掉 Ray 依赖

通过 StandaloneProxy 适配层让 .remote() 调用在单机模式下透明降级为
asyncio 协程调用，7 个 Actor 和 workflow task 均可在纯 asyncio 环境运行，
启动快、资源占用低。分布式模式行为完全不变。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

kilostar/api/__init__.py

@@ -19,7 +19,10 @@ from fastapi import FastAPI, WebSocket, Request
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import FileResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
-from ray import serve
+
+_STANDALONE = os.environ.get("KILOSTAR_MODE", "distributed") == "standalone"
+if not _STANDALONE:
+    from ray import serve
 
 from .agent import agent_router
 from .auth import auth_router
@@ -176,10 +179,11 @@ else:
     )
 
 
-@serve.deployment
-@serve.ingress(app)
-class KiloStarGateway:
-    gateway: Dict[str, WebSocket]
+if not _STANDALONE:
+    @serve.deployment
+    @serve.ingress(app)
+    class KiloStarGateway:
+        gateway: Dict[str, WebSocket]
 
-    def __init__(self):
-        self.gateway = {}
+        def __init__(self):
+            self.gateway = {}