Add device labels to occupancy alerts — include who is present

NET_ALERTER_DEVICE_LABELS=MAC=Name,MAC=Name maps known devices to
friendly names. OCCUPIED alerts now show which devices are present.
Falls back to vendor string then MAC tail if no label configured.

net_alerter/net_alerter.py

@@ -121,6 +121,7 @@ MOBILE_DEVICE_OUIS = {
 # Personal device tracking
 personal_devices = set()  # {mac: ...} of detected personal device MACs
 personal_names = set()  # {name: ...} device names for auto-discovery via mDNS
+device_labels: dict = {}  # {normalized_mac: friendly_name} from NET_ALERTER_DEVICE_LABELS
 personal_lock = threading.Lock()
 location_occupancy = "UNKNOWN"  # Current location state: VACANT, OCCUPIED, UNKNOWN
 occupancy_lock = threading.Lock()
@@ -664,6 +665,17 @@ def load_personal_macs_from_env() -> None:
             for name in names:
                 personal_names.add(name)
         
+        # Load device labels (MAC=Name pairs for readable alerts)
+        labels_str = os.getenv("NET_ALERTER_DEVICE_LABELS", "")
+        if labels_str.strip():
+            for pair in labels_str.split(","):
+                if "=" not in pair:
+                    continue
+                mac_part, _, name_part = pair.partition("=")
+                normalized = _normalize_mac(mac_part.strip())
+                if normalized:
+                    device_labels[normalized] = name_part.strip()
+
         # Log summary
         if personal_devices or personal_names:
             logging.info(f"Loaded {len(personal_devices)} personal device MAC(s) and {len(personal_names)} personal name(s)")
@@ -900,7 +912,15 @@ def _update_occupancy_state_unlocked() -> None:
 
     # Fire alert on all transitions including startup UNKNOWN → OCCUPIED
     if new_occupancy != location_occupancy:
-        msg = f"[NET] Location: {new_occupancy}"
+        if new_occupancy == "OCCUPIED":
+            present = []
+            for mac, dev in known_devices.items():
+                if not dev.get('departing', False) and dev['ip'] not in infrastructure_ips:
+                    label = device_labels.get(mac) or dev.get('vendor') or mac[-8:]
+                    present.append(label)
+            msg = f"[NET] Location: OCCUPIED ({', '.join(present)})"
+        else:
+            msg = f"[NET] Location: VACANT"
         logging.info(msg)
         send_alert(msg)