Initial commit: LAN Checker

Network health monitoring script with MQTT reporting for Home Assistant.
- Ping, HTTP, and SNMP checkers
- MQTT Discovery for automatic entity creation
- Configurable check intervals

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

checkers/__init__.py

@@ -0,0 +1,9 @@
+from .ping import PingChecker
+from .http import HttpChecker
+from .snmp import SnmpChecker
+
+CHECKERS = {
+    "ping": PingChecker,
+    "http": HttpChecker,
+    "snmp": SnmpChecker,
+}