fix(xiaomi-tokenplan): region selector, key validation, multi-connection (#2251)

- Add top-level regions array so Add/Edit modals render region <Select>
- EditConnectionModal: load/persist region generically for region-aware providers
- validate: accept 403 for xiaomi-tokenplan valid keys, add 8s fetch timeout
- Remove single-connection guard for compatible/embedding nodes

Co-authored-by: MiQieR <122154116+MiQieR@users.noreply.github.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/providers/registry/xiaomi-tokenplan.js

@@ -21,6 +21,11 @@ export default {
   },
   category: "apikey",
   hasProviderSpecificData: true,
+  regions: [
+    { id: "sgp", label: "Singapore (新加坡)" },
+    { id: "cn", label: "China (中国大陆)" },
+    { id: "ams", label: "Amsterdam (阿姆斯特丹)" },
+  ],
   defaultRegion: "sgp",
   transport: {
     baseUrl: "https://token-plan-sgp.xiaomimimo.com/v1/chat/completions",