Refactor DeerFlow to use Gateway's LangGraph-compatible API

- Updated documentation and comments to reflect the transition from LangGraph Server to Gateway.
- Changed default URLs in ChannelManager and tests to point to Gateway.
- Removed references to LangGraph Server in deployment scripts and configurations.
- Updated Nginx configuration to route API traffic to Gateway.
- Adjusted frontend configurations to utilize Gateway's API.
- Removed LangGraph service from Docker Compose files, consolidating services under Gateway.
- Added regression tests to ensure Gateway integration works as expected.

Co-authored-by: Copilot <copilot@github.com>

scripts/docker.sh

@@ -148,18 +148,15 @@ init() {
 }
 
 # Start Docker development environment
-# Usage: start [--gateway]
 start() {
     local sandbox_mode
     local services
-    local gateway_mode=false
 
-    # Check for --gateway flag
-    for arg in "$@"; do
-        if [ "$arg" = "--gateway" ]; then
-            gateway_mode=true
-        fi
-    done
+    if [ "$#" -gt 0 ]; then
+        echo -e "${YELLOW}Unknown option for start: $1${NC}"
+        echo "Usage: $0 start"
+        exit 1
+    fi
 
     echo "=========================================="
     echo "  Starting DeerFlow Docker Development"
@@ -168,21 +165,12 @@ start() {
 
     sandbox_mode="$(detect_sandbox_mode)"
 
-    if $gateway_mode; then
-        services="frontend gateway nginx"
-        if [ "$sandbox_mode" = "provisioner" ]; then
-            services="frontend gateway provisioner nginx"
-        fi
-    else
-        services="frontend gateway langgraph nginx"
-        if [ "$sandbox_mode" = "provisioner" ]; then
-            services="frontend gateway langgraph provisioner nginx"
-        fi
+    services="frontend gateway nginx"
+    if [ "$sandbox_mode" = "provisioner" ]; then
+        services="frontend gateway provisioner nginx"
     fi
 
-    if $gateway_mode; then
-        echo -e "${BLUE}Runtime: Gateway mode (experimental) — no LangGraph container${NC}"
-    fi
+    echo -e "${BLUE}Runtime: Gateway embedded agent runtime${NC}"
     echo -e "${BLUE}Detected sandbox mode: $sandbox_mode${NC}"
     if [ "$sandbox_mode" = "provisioner" ]; then
         echo -e "${BLUE}Provisioner enabled (Kubernetes mode).${NC}"
@@ -232,12 +220,6 @@ start() {
         fi
     fi
 
-    # Set nginx routing for gateway mode (envsubst in nginx container)
-    if $gateway_mode; then
-        export LANGGRAPH_UPSTREAM=gateway:8001
-        export LANGGRAPH_REWRITE=/api/
-    fi
-
     echo "Building and starting containers..."
     cd "$DOCKER_DIR" && $COMPOSE_CMD up --build -d --remove-orphans $services
     echo ""
@@ -247,12 +229,8 @@ start() {
     echo ""
     echo "  🌐 Application: http://localhost:2026"
     echo "  📡 API Gateway: http://localhost:2026/api/*"
-    if $gateway_mode; then
-        echo "  🤖 Runtime:     Gateway embedded"
-        echo "  API:            /api/langgraph/* → Gateway (compat)"
-    else
-        echo "  🤖 LangGraph:   http://localhost:2026/api/langgraph/*"
-    fi
+    echo "  🤖 Runtime:     Gateway embedded"
+    echo "  API:            /api/langgraph/* → Gateway"
     echo ""
     echo "  📋 View logs: make docker-logs"
     echo "  🛑 Stop:      make docker-stop"
@@ -332,7 +310,6 @@ help() {
     echo "Commands:"
     echo "  init              - Pull the sandbox image (speeds up first Pod startup)"
     echo "  start             - Start Docker services (auto-detects sandbox mode from config.yaml)"
-    echo "  start --gateway   - Start without LangGraph container (Gateway mode, experimental)"
     echo "  restart           - Restart all running Docker services"
     echo "  logs [option] - View Docker development logs"
     echo "                  --frontend   View frontend logs only"