Make RFID failure non-fatal (self-test retries, 4MHz clock, diagnostic log), add beginner Wi-Fi guide + RFID troubleshooting to README

main/scryfall_client.c

@@ -360,16 +360,16 @@ static void net_task(void *arg)
 #ifndef CONFIG_MTG_WIFI_SSID
 #error "Missing CONFIG_MTG_WIFI_SSID"
 #endif
-    if (strlen(CONFIG_MTG_WIFI_SSID) > 0) {
+    if (wifi_manager_sta_configured()) {
         if (wifi_manager_wait_connected(pdMS_TO_TICKS(60000)) != ESP_OK) {
             ESP_LOGW(TAG, "Wi-Fi connect timed out, continuing without network");
+        } else {
+#ifdef CONFIG_MTG_SCAN_PREFETCH
+            prefetch_mappings();
+#endif
         }
     }
 
-#ifdef CONFIG_MTG_SCAN_PREFETCH
-    prefetch_mappings();
-#endif
-
     while (1) {
         fetch_request_t req;
         BaseType_t got = xQueueReceive(s_fetch_queue, &req, portMAX_DELAY);