fix(chat): 前端审计修复——预览契约改HTML/状态机统一/进度错误持久化/chat_state.js抽取

- app.py: /result/preview 返回渲染 HTML(HTMLResponse) 而非 {html} JSON；新增 /chat_state.js 静态路由；预览缺失返回 404(RESULT_NOT_FOUND)
- chat.html: currentProject 统一为 draftProject；新会话继承已选项目(§4.2)；上传区显隐/类型映射/抽屉脏检测改用 GenesisState；loadSession 按 role 渲染 progress/error；加 h1 标题
- chat_state.js(新): 抽取 autoBindProject/shouldHideUploadSelect/resolveUploadType/computeDrawerSnapshot/isDrawerDirty/buildWelcome 纯函数(U+1 分隔符)
- agent.py: 新增 _persist_progress/_store_error，进度与错误以 role 入库(重载可见)
- 测试: test_chat_state.js(11 passed) + test_frontend_audit_fixes.py(5) + 修正 test_server_api 旧 JSON 契约断言；全量 pytest 568 passed / 99.06%

src/genesis/server/app.py

@@ -110,6 +110,13 @@ def create_app(
     def index():
         return chat_html
 
+    @app.get("/chat_state.js")
+    def chat_state_js():
+        p = static_dir / "chat_state.js"
+        if not p.exists():
+            raise _error(404, "NOT_FOUND", "chat_state.js 不存在")
+        return FileResponse(p, media_type="application/javascript")
+
     # ---------- 项目配置 ----------
 
     @app.post("/api/projects")
@@ -266,10 +273,13 @@ def create_app(
 
     # ---------- 结果 ----------
 
-    @app.get("/api/sessions/{sid}/result/preview")
+    @app.get("/api/sessions/{sid}/result/preview", response_class=HTMLResponse)
     def result_preview(sid: str):
-        html = service.result_preview(sid)
-        return {"html": html}
+        try:
+            html = service.result_preview(sid)
+        except ServiceStepError:
+            raise _error(404, "RESULT_NOT_FOUND", "结果文档不存在")
+        return HTMLResponse(html)
 
     @app.get("/api/sessions/{sid}/result/download")
     def result_download(sid: str):