Merge refactor/config-deerflow-context into release/2.0-rc

Cherry-pick PR #2271's config refactor onto release/2.0-rc.
Used 'git merge -X theirs' to auto-resolve content conflicts in favor of
the PR's design (frozen AppConfig + explicit-parameter passing).

Limitations:
- Release-only changes that overlapped with PR's refactor in 119 files
  are NOT preserved — those files reflect PR's version. Follow-up commits
  on this branch will need to re-apply release-only modifications where
  meaningful.
- See PR #2271 for design rationale.

docker/docker-compose.yaml

@@ -110,6 +110,58 @@ services:
       - deer-flow
     restart: unless-stopped
 
+  # ── LangGraph Server ───────────────────────────────────────────────────────
+  # TODO: switch to langchain/langgraph-api (licensed) once a license key is available.
+  # For now, use `langgraph dev` (no license required) with the standard backend image.
+  langgraph:
+    build:
+      context: ../
+      dockerfile: backend/Dockerfile
+      args:
+        APT_MIRROR: ${APT_MIRROR:-}
+        UV_IMAGE: ${UV_IMAGE:-ghcr.io/astral-sh/uv:0.7.20}
+        UV_INDEX_URL: ${UV_INDEX_URL:-https://pypi.org/simple}
+        UV_EXTRAS: ${UV_EXTRAS:-}
+    container_name: deer-flow-langgraph
+    command: sh -c 'cd /app/backend && args="--no-browser --no-reload --host 0.0.0.0 --port 2024 --n-jobs-per-worker $${LANGGRAPH_JOBS_PER_WORKER:-10}" && if [ "$${LANGGRAPH_ALLOW_BLOCKING:-0}" = "1" ]; then args="$$args --allow-blocking"; fi && uv run langgraph dev $$args'
+    volumes:
+      - ${DEER_FLOW_CONFIG_PATH}:/app/backend/config.yaml:ro
+      - ${DEER_FLOW_EXTENSIONS_CONFIG_PATH}:/app/backend/extensions_config.json:ro
+      - ${DEER_FLOW_HOME}:/app/backend/.deer-flow
+      - ../skills:/app/skills:ro
+      - ../backend/.langgraph_api:/app/backend/.langgraph_api
+      # DooD: same as gateway
+      - ${DEER_FLOW_DOCKER_SOCKET}:/var/run/docker.sock
+      # CLI auth directories for auto-auth (Claude Code + Codex CLI)
+      - type: bind
+        source: ${HOME:?HOME must be set}/.claude
+        target: /root/.claude
+        read_only: true
+        bind:
+          create_host_path: true
+      - type: bind
+        source: ${HOME:?HOME must be set}/.codex
+        target: /root/.codex
+        read_only: true
+        bind:
+          create_host_path: true
+    environment:
+      - CI=true
+      - DEER_FLOW_HOME=/app/backend/.deer-flow
+      - DEER_FLOW_CONFIG_PATH=/app/backend/config.yaml
+      - DEER_FLOW_EXTENSIONS_CONFIG_PATH=/app/backend/extensions_config.json
+      - DEER_FLOW_HOST_BASE_DIR=${DEER_FLOW_HOME}
+      - DEER_FLOW_HOST_SKILLS_PATH=${DEER_FLOW_REPO_ROOT}/skills
+      - DEER_FLOW_SANDBOX_HOST=host.docker.internal
+      # LangSmith tracing: set LANGSMITH_TRACING=true and LANGSMITH_API_KEY in .env to enable.
+    env_file:
+      - ../.env
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
+    networks:
+      - deer-flow
+    restart: unless-stopped
+
   # ── Sandbox Provisioner (optional, Kubernetes mode) ────────────────────────
   provisioner:
     build: