feat: add Tencent Cloud TokenHub provider with auto model sync

Fetch GET /v1/models on provider/key switch, activate online chat models,
and accept HERMIT_/CST_ key env aliases plus tencent* provider names.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/model_registry.c

@@ -545,6 +545,11 @@ const char *cst_models_load_error(void) {
 const cst_provider_t *cst_provider_find(const char *name) {
   if (!name || !name[0])
     return NULL;
+  /* Friendly aliases for 腾讯云 TokenHub. */
+  if (strcmp(name, "tencent") == 0 || strcmp(name, "tencentcloud") == 0 ||
+      strcmp(name, "token-hub") == 0 || strcmp(name, "腾讯") == 0 ||
+      strcmp(name, "腾讯云") == 0)
+    name = "tokenhub";
   pthread_mutex_lock(&g_mu);
   ensure_locked();
   prov_t *p = prov_by_name(name);