fix: reset_reason aus system/info entfernen

Das Feld lieferte ohnehin nur den festen String "unknown" - kein SDK-Aufruf
lieferte je einen echten Reset-Grund. README/hardware-checklist erwähnten
es nicht.

src/net/nl_api.c

@@ -245,7 +245,6 @@ static void handle_info(const nl_api_ctx_t *ctx, nl_api_response_t *resp)
         cJSON_AddNullToObject(w, "error");
     cJSON_AddNumberToObject(o, "uptime", in.uptime_s);
     cJSON_AddNumberToObject(o, "free_heap", in.free_heap);
-    cJSON_AddStringToObject(o, "reset_reason", "unknown");
     if (in.last_ota_error)
         cJSON_AddStringToObject(o, "last_ota_error", in.last_ota_error);
     else

test/test_api.c

@@ -207,7 +207,7 @@ static void test_info_is_open(void)
     TEST_ASSERT_TRUE(cJSON_IsNull(cJSON_GetObjectItem(w, "error")));
     TEST_ASSERT_EQUAL_INT(123, field("uptime")->valueint);
     TEST_ASSERT_EQUAL_INT(40000, field("free_heap")->valueint);
-    TEST_ASSERT_EQUAL_STRING("unknown", cJSON_GetStringValue(field("reset_reason")));
+    TEST_ASSERT_NULL(cJSON_GetObjectItem(doc, "reset_reason"));
     TEST_ASSERT_TRUE(cJSON_IsNull(field("last_ota_error")));
 }