feat: improve IoT device detection via two-phase scan and mDNS discovery

- Two-phase nmap: ARP sweep first to find all alive hosts (incl. IoT with
  no open TCP ports), then port scan only alive hosts
- mDNS/Bonjour discovery via zeroconf for Shelly, ESPHome, HomeKit devices
- Add CoAP ports (5683, 5684, 4915) to port scan and IoT type hints
- Expand MAC OUI table with Shelly, Espressif, Sonoff, Tapo, Hue, IKEA, Tuya
- IoT vendor MAC takes precedence over generic HTTP port type hints
- Reorder suggest_node_type priority: iot now beats server

backend/tests/test_fingerprint.py

@@ -131,3 +131,45 @@ def test_suggest_node_type_camera_from_signature():
     ]):
         result = suggest_node_type([{"port": 554, "protocol": "tcp"}])
         assert result == "camera"
+
+
+# ── IoT detection ─────────────────────────────────────────────────────────────
+
+def test_suggest_node_type_iot_from_mqtt_port():
+    result = suggest_node_type([{"port": 1883, "protocol": "tcp"}])
+    assert result == "iot"
+
+
+def test_suggest_node_type_iot_from_coap_port():
+    result = suggest_node_type([{"port": 5683, "protocol": "tcp"}])
+    assert result == "iot"
+
+
+def test_suggest_node_type_iot_from_esphome_port():
+    result = suggest_node_type([{"port": 6052, "protocol": "tcp"}])
+    assert result == "iot"
+
+
+def test_suggest_node_type_shelly_mac_overrides_http_port():
+    # Shelly exposes port 80 (would suggest "server") but MAC identifies it as IoT
+    result = suggest_node_type([{"port": 80, "protocol": "tcp"}], mac="34:94:54:aa:bb:cc")
+    assert result == "iot"
+
+
+def test_suggest_node_type_espressif_mac_returns_iot():
+    result = suggest_node_type([], mac="a0:20:a6:11:22:33")
+    assert result == "iot"
+
+
+def test_suggest_node_type_tuya_mac_returns_iot():
+    result = suggest_node_type([{"port": 80, "protocol": "tcp"}], mac="d8:f1:5b:aa:bb:cc")
+    assert result == "iot"
+
+
+def test_suggest_node_type_iot_wins_over_server_when_mqtt_present():
+    # MQTT port + HTTP port → iot wins (iot is higher priority than server now)
+    result = suggest_node_type([
+        {"port": 80, "protocol": "tcp"},
+        {"port": 1883, "protocol": "tcp"},
+    ])
+    assert result == "iot"