feat: M1 — 立项→写章草稿(SSE)→自动保存；连一家 provider

- 薄自建 LLM 网关：OpenAI 兼容适配器(DeepSeek) + instructor 结构化输出 + usage_ledger 记账 + 档位路由
- 记忆服务 assemble：确定性选择(显式+主角+近况) + 渲染卡 + 缓存断点(中性文本)
- LangGraph 写章节点 + Postgres checkpointer + SSE 归一(token/done/error)
- API：立项 + 写章 draft(SSE) + PUT 自动保存 + 提供商凭据(Fernet 加密/测试连接)
- 前端：AppShell + 作品库 + 5 步立项向导 + 写作工作台(流式打字机+自动保存) + 设置页
- M1 E2E：真实 DB + mock 网关零 token 走通闭环

packages/llm_gateway/tests/fakes.py

@@ -0,0 +1,56 @@
+"""网关单测替身（mock provider + 内存 ledger）——不碰真实 API / DB。
+
+放在独立模块（非 conftest）以便测试用绝对导入 `from fakes import ...`；
+本目录无 __init__.py（避免与顶层 tests 包同名冲突），故走 pytest 路径注入。
+"""
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator
+
+from ww_llm_gateway.adapters.base import (
+    Capabilities,
+    ProviderResult,
+    ProviderUsage,
+    StreamChunk,
+)
+from ww_llm_gateway.routing import Route
+from ww_llm_gateway.types import LlmRequest, Scope, Tier, Usage
+
+
+class FakeAdapter:
+    provider = "deepseek"
+
+    def __init__(self, text: str = "hello world", deltas: list[str] | None = None) -> None:
+        self.text = text
+        self.deltas = deltas if deltas is not None else ["hel", "lo ", "world"]
+        self.complete_calls = 0
+        self.stream_calls = 0
+
+    def capabilities(self) -> Capabilities:
+        return Capabilities(structured_output=True, prefix_cache=True)
+
+    async def complete(self, req: LlmRequest, model: str) -> ProviderResult:
+        self.complete_calls += 1
+        return ProviderResult(
+            text=self.text,
+            usage=ProviderUsage(input_tokens=100, output_tokens=50),
+        )
+
+    async def stream(self, req: LlmRequest, model: str) -> AsyncIterator[StreamChunk]:
+        self.stream_calls += 1
+        for d in self.deltas:
+            yield StreamChunk(text=d)
+        yield StreamChunk(usage=ProviderUsage(input_tokens=100, output_tokens=50))
+
+
+class FakeLedger:
+    def __init__(self) -> None:
+        self.records: list[Usage] = []
+
+    async def record(self, scope: Scope, usage: Usage) -> None:
+        self.records.append(usage)
+
+
+def fake_route(tier: Tier) -> Route:
+    return Route(provider="deepseek", model="deepseek-chat")