feat: resilient boot + full polish pass

Firmware:
- nfc_engine: add nfc_engine_try_init() (non-fatal, sets s_pn532_ready),
  nfc_engine_try_reattach() (soft re-init, skips bus re-init),
  nfc_engine_is_ready() accessor
- main: replace ESP_ERROR_CHECK(nfc_engine_init) with nfc_engine_try_init;
  device boots and serves web UI even with no PN532 connected
- app_net: add reconnect_task — every 5s retries nfc_engine_try_reattach()
  and broadcasts {"channel":"pn532","payload":{"connected":true}} over WS
- app_net: scan_loop_task skips polling when !nfc_engine_is_ready()
- app_net/api_status: always emit pn532Connected bool; null-guard pn532 fw object
- find_sector_hit / program_classic_snapshot_locked: null-guard cJSON array items
- session_capture: abort if xSemaphoreCreateMutex() returns NULL

Web:
- NfcWsContext: track pn532Connected state from WS pn532 channel + status fetch on connect
- App.tsx: live HeaderBadge (LIVE/NO RF/WAIT) replacing static text
- Dashboard: READY/SEARCHING pill with fw version when available
- api.ts: add pn532Connected to Status type
- toast.tsx: fix ID collision (Date.now + Math.random)
- Capture: surface status fetch errors
- ReadAnalyze: add error feedback for readUl when no data returned
- WriteClone: busy state on both write buttons
- RawConsole: toast when frame returns error not response
- Emulate: validate hex before send (non-empty, even length, hex chars only)
- Brute: warn and skip invalid custom key lines

Made-with: Cursor

firmware/components/nfc_engine/nfc_engine.c

@@ -8,6 +8,9 @@
 static const char *TAG = "nfc_engine";
 
 static uint8_t s_tg = 1;
+static volatile bool s_pn532_ready = false;
+
+bool nfc_engine_is_ready(void) { return s_pn532_ready; }
 
 static void hint_type(nfc_tag_info_t *t)
 {
@@ -102,9 +105,51 @@ esp_err_t nfc_engine_init(void)
     if (pn532_rf_max_retries() != ESP_OK) {
         ESP_LOGW(TAG, "RF max retries config failed");
     }
+    s_pn532_ready = true;
     return ESP_OK;
 }
 
+bool nfc_engine_try_init(void)
+{
+    esp_err_t e = pn532_core_init();
+    if (e != ESP_OK) {
+        ESP_LOGW(TAG, "PN532 not found (%s) — AP running, will retry every 5 s", esp_err_to_name(e));
+        s_pn532_ready = false;
+        return false;
+    }
+    e = pn532_sam_config_normal();
+    if (e != ESP_OK) {
+        ESP_LOGW(TAG, "SAM config: %s", esp_err_to_name(e));
+    }
+    uint8_t ic = 0, hi = 0, lo = 0;
+    if (pn532_get_firmware_version(&ic, &hi, &lo) == ESP_OK) {
+        ESP_LOGI(TAG, "PN532 fw ic=0x%02x %u.%u", ic, hi, lo);
+    }
+    if (pn532_rf_max_retries() != ESP_OK) {
+        ESP_LOGW(TAG, "RF max retries config failed");
+    }
+    s_pn532_ready = true;
+    return true;
+}
+
+bool nfc_engine_try_reattach(void)
+{
+    /* Transport already open — just ping the chip and re-apply configuration. */
+    esp_err_t e = pn532_sam_config_normal();
+    if (e != ESP_OK) {
+        return false;
+    }
+    uint8_t ic = 0, hi = 0, lo = 0;
+    if (pn532_get_firmware_version(&ic, &hi, &lo) == ESP_OK) {
+        ESP_LOGI(TAG, "PN532 reattached ic=0x%02x %u.%u", ic, hi, lo);
+    }
+    if (pn532_rf_max_retries() != ESP_OK) {
+        ESP_LOGW(TAG, "RF max retries config failed");
+    }
+    s_pn532_ready = true;
+    return true;
+}
+
 esp_err_t nfc_poll_passive_target(nfc_tag_info_t *out)
 {
     if (!out) {