Initial commit: esphome-xtool-ap2 ESPHome component

Control one or two xTool SafetyPro AP2 air purifiers over BLE and expose them to Home Assistant via an ESP32 (the ap2_hub external component): per-slot fan control with live gear sync, runtime-settable flash-persisted MACs, an on-device scanner, M9033 status polling (filter life, serial, firmware), buzzer control, and BLE bonding. Includes the PC debug tool (tools/ap2_ble.py) and the reverse-engineered protocol spec (SPEC.md).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

components/ap2_hub/ap2_probe.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include "esphome/components/esp32_ble_client/ble_client_base.h"
+#include "ap2_protocol.h"
+
+#include <esp_gattc_api.h>
+#include <string>
+
+namespace esphome {
+namespace ap2_hub {
+
+class AP2Hub;
+
+/* Transient BLE client the hub uses during a scan: connect to one candidate,
+ * look for the Nordic-UART service, send M99, and confirm an AP2 by its reply.
+ * Every probe ends at ClientState::IDLE, which is the single signal back to the
+ * hub that the prober is free for the next candidate. */
+class AP2ProbeClient : public esp32_ble_client::BLEClientBase {
+ public:
+  void set_hub(AP2Hub *hub) { this->hub_ = hub; }
+
+  void start_probe(uint64_t mac, esp_ble_addr_type_t type);
+  void abort_probe();
+
+  bool gattc_event_handler(esp_gattc_cb_event_t event, esp_gatt_if_t gattc_if,
+                           esp_ble_gattc_cb_param_t *param) override;
+  void set_state(espbt::ClientState st) override;
+
+ protected:
+  AP2Hub *hub_{nullptr};
+  uint16_t rx_handle_{0};
+  uint16_t tx_handle_{0};
+  uint16_t ccc_handle_{0};
+  bool active_{false};
+  bool confirmed_{false};
+  std::string fw_;
+};
+
+}  // namespace ap2_hub
+}  // namespace esphome