Add SQLite OUI database lookup to net_alerter

- lookup_oui() now tries SQLite first (/opt/net_alerter/oui.db)
- Falls back to inline OUI_DICT if DB missing or query fails
- No network calls, local SQLite reads only
- Debug-level logging for failures (no output noise)

net_alerter/net_alerter.py

@@ -20,6 +20,7 @@ import threading
 import time
 import urllib.parse
 import urllib.request
+import sqlite3
 from pathlib import Path
 
 # --- Config (from .env or env vars) ---
@@ -27,6 +28,7 @@ MATRIX_HOMESERVER = ""
 MATRIX_ACCESS_TOKEN = ""
 MATRIX_ROOM_ID = ""
 LOG_FILE = "/opt/net_alerter/net_alerter.log"
+OUI_DB_PATH = "/opt/net_alerter/oui.db"
 
 known_devices = {}  # {mac: {ip, hostname, vendor, first_seen, last_seen, infrastructure (opt)}}
 known_lock = threading.Lock()
@@ -279,14 +281,29 @@ def load_env():
 def lookup_oui(mac: str) -> str:
     """
     Look up OUI vendor from MAC address (first 3 octets).
-    Uses inline dictionary of top 200 common vendors.
+    Tries SQLite database first, falls back to inline dictionary.
     Returns vendor name or 'unknown' if not found.
     """
     if not mac or mac == "00:00:00:00:00:00":
         return "unknown"
 
-    oui_prefix = mac[:8].replace(":", "").upper()
-    return OUI_DICT.get(oui_prefix, "unknown")
+    # Try database first
+    oui_prefix = mac[:8].lower()
+    try:
+        conn = sqlite3.connect(OUI_DB_PATH, timeout=1)
+        conn.row_factory = sqlite3.Row
+        cursor = conn.cursor()
+        result = cursor.execute("SELECT vendor FROM oui WHERE prefix = ?", (oui_prefix,)).fetchone()
+        conn.close()
+        if result:
+            return result['vendor']
+    except Exception:
+        # Log at DEBUG only, no output noise
+        logging.debug(f"OUI database lookup failed for {oui_prefix}", exc_info=False)
+    
+    # Fall back to inline dictionary
+    oui_prefix_upper = oui_prefix.replace(":", "").upper()
+    return OUI_DICT.get(oui_prefix_upper, "unknown")
 
 
 def seed_from_arp_cache():