Add Olimex ESP32-C6-EVB + PN532 NFC driver and web UI

- New driver: app/drivers/olimex_esp32_c6_evb_pn532/
  - Full relay/input control (inherits base behaviour)
  - get_nfc_status(), get_nfc_config(), set_nfc_config() methods
  - manifest.json with NFC hardware metadata (UEXT1 pins, card standard)

- NFC management routes (boards.py):
  - GET  /boards/<id>/nfc            — management page
  - GET  /boards/<id>/nfc/status_json — live JSON (polled every 3 s)
  - POST /boards/<id>/nfc/config     — save auth UID / relay / timeout
  - POST /boards/<id>/nfc/enroll     — enrol last-seen card with one click

- New template: templates/boards/nfc.html
  - Live reader status (PN532 ready, access state, last UID)
  - Quick Enroll: present card → Refresh → Enrol in one click
  - Manual Settings: type/paste UID, pick relay, set absence timeout

- detail.html: NFC Access Control button shown for pn532 board type

app/templates/boards/detail.html

@@ -20,6 +20,11 @@
   </div>
   {% if current_user.is_admin() %}
   <div class="d-flex gap-2">
+    {% if board.board_type == 'olimex_esp32_c6_evb_pn532' %}
+    <a href="{{ url_for('boards.nfc_management', board_id=board.id) }}" class="btn btn-outline-primary">
+      <i class="bi bi-credit-card-2-front me-1"></i> NFC Access Control
+    </a>
+    {% endif %}
     <a href="{{ url_for('boards.edit_entities', board_id=board.id) }}" class="btn btn-outline-info">
       <i class="bi bi-palette me-1"></i> Configure Entities
     </a>