feat: add nginx reversed proxy (#15)

* docs: add nginx reverse proxy documentation

Add comprehensive nginx configuration documentation to README including:
- Production deployment instructions with step-by-step setup
- Architecture diagram showing traffic routing between services
- Nginx features: unified entry point, CORS handling, SSE support
- Updated project structure with nginx.conf and service ports

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* feat: implement nginx

---------

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/src/gateway/app.py

@@ -3,10 +3,16 @@ from collections.abc import AsyncGenerator
 from contextlib import asynccontextmanager
 
 from fastapi import FastAPI
-from fastapi.middleware.cors import CORSMiddleware
 
 from src.gateway.config import get_gateway_config
-from src.gateway.routers import artifacts, models, proxy
+from src.gateway.routers import artifacts, models
+
+# Configure logging
+logging.basicConfig(
+    level=logging.INFO,
+    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+    datefmt="%Y-%m-%d %H:%M:%S",
+)
 
 logger = logging.getLogger(__name__)
 
@@ -16,7 +22,6 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
     """Application lifespan handler."""
     config = get_gateway_config()
     logger.info(f"Starting API Gateway on {config.host}:{config.port}")
-    logger.info(f"Proxying to LangGraph server at {config.langgraph_url}")
 
     # Initialize MCP tools at startup
     try:
@@ -28,8 +33,6 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
 
     yield
     logger.info("Shutting down API Gateway")
-    # Close the shared HTTP client
-    await proxy.close_http_client()
 
 
 def create_app() -> FastAPI:
@@ -41,19 +44,12 @@ def create_app() -> FastAPI:
 
     app = FastAPI(
         title="DeerFlow API Gateway",
-        description="API Gateway for DeerFlow - proxies to LangGraph Server and provides custom endpoints",
+        description="API Gateway for DeerFlow - provides custom endpoints (models, artifacts). LangGraph requests are handled by nginx.",
         version="0.1.0",
         lifespan=lifespan,
     )
 
-    # Add CORS middleware
-    app.add_middleware(
-        CORSMiddleware,
-        allow_origins=["*"],
-        allow_credentials=True,
-        allow_methods=["*"],
-        allow_headers=["*"],
-    )
+    # CORS is handled by nginx - no need for FastAPI middleware
 
     # Include routers
     # Models API is mounted at /api/models
@@ -62,9 +58,6 @@ def create_app() -> FastAPI:
     # Artifacts API is mounted at /api/threads/{thread_id}/artifacts
     app.include_router(artifacts.router)
 
-    # Proxy router handles all LangGraph paths (must be last due to catch-all)
-    app.include_router(proxy.router)
-
     @app.get("/health")
     async def health_check() -> dict:
         """Health check endpoint."""