feat(travel): 接入远端 AI 推荐服务，支持 GLM real 模式与本地静默回退

- createPlan 在配置 VITE_TRAVEL_ASSISTANT_API_BASE_URL 时调用 FastAPI 推荐服务
  做无坐标选点，路线/交通/时长仍由本机核算；远端不可用即静默回退本地规划
- 放开 loadPlan 对远端行程的回读限制（原 AI 冻结期禁用），行程页跳转不再丢行程
- planner/assistant 文案按是否启用远端如实切换，不再谎称「本期不调用 AI」
- 新增远端接通/回退/候选载荷单测；server/README 更新联调与 real 模式说明
- .env.development 默认指向已部署推荐服务；server/.env.example 补 GLM 示例

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.env.development

@@ -1 +1,8 @@
 # 在开发时进行加载
+
+# Deployed travel recommender (FastAPI, real GLM) on the gml box, exposed via
+# Tailscale Funnel. The /travel/ prefix is stripped by Tailscale before reaching
+# the app, so the client calls .../travel/api/v1/plans. Set to empty (or stop the
+# service) to use the deterministic local planner; on any remote error the client
+# silently falls back to local so the demo never breaks.
+VITE_TRAVEL_ASSISTANT_API_BASE_URL=https://desktop-gml.tailc2083d.ts.net/travel