feat: mark Modbus connection loss in InfluxDB

SolarEdge firmware is known to silently drop the Modbus TCP listener
(port refuses connections while still shown as enabled). Write a
connection_state=1 point on first failed poll and 0 on recovery so the
outage is visible in Grafana instead of just a data gap.

ConnectionException is re-raised from read() - it is fatal for the
whole cycle, not a flaky single block. Marker points carry no tags
(registers unreadable during outage), so the tile query skips the
serial filter.

Also includes threshold tweaks on the power stat tiles.

solaredge_modbus_mqtt.py

@@ -81,15 +81,24 @@ if __name__ == '__main__':
         unit=config['modbus']['unit']
     )
 
+    modbus_ok = True
+    measurement = config['influx'].get('measurement', 'solaredge')
+
     while True:
         try:
             raw = inverter.read()
+            if not modbus_ok:
+                publish(to_line_protocol({'connection_state': 0}, measurement), config['influx'])
+                modbus_ok = True
             solar_data = SolarData(raw)
-            line = to_line_protocol(solar_data.data, config['influx'].get('measurement', 'solaredge'))
+            line = to_line_protocol(solar_data.data, measurement)
             if line:
                 publish(line, config['influx'])
         except ConnectionException as err:
             print('Cannot connect to SolarEdge Modbus server on {0}:{1}, error: {2}'.format(
                 config['modbus']['host'], config['modbus']['port'], err))
+            if modbus_ok:
+                publish(to_line_protocol({'connection_state': 1}, measurement), config['influx'])
+                modbus_ok = False
 
         time.sleep(config['poll_interval'])