Add error handling and logging to monitoring supervisor

Improved startup reliability and debugging for SNMP pollers:
- Added try/rescue blocks around monitor and poller startup
- Added logging for successful startup and errors
- Added error logging to PollerWorker's perform_poll
- Added debug logging for successful sensor/interface polls

This will help identify issues when pollers fail to start or
encounter errors during polling, which was causing silent failures
where sensors weren't being collected.

lib/towerops/monitoring/supervisor.ex

@@ -9,6 +9,8 @@ defmodule Towerops.Monitoring.Supervisor do
   alias Towerops.Snmp.PollerSupervisor
   alias Towerops.Snmp.PollerWorker
 
+  require Logger
+
   def start_link(init_arg) do
     Supervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
   end
@@ -33,8 +35,22 @@ defmodule Towerops.Monitoring.Supervisor do
         Task.start(fn ->
           # Wait briefly for the supervisor tree to be fully initialized
           Process.sleep(100)
-          start_all_monitors()
-          start_all_snmp_pollers()
+
+          try do
+            start_all_monitors()
+            Logger.info("Started all equipment monitors")
+          rescue
+            error ->
+              Logger.error("Failed to start monitors: #{inspect(error)}")
+          end
+
+          try do
+            start_all_snmp_pollers()
+            Logger.info("Started all SNMP pollers")
+          rescue
+            error ->
+              Logger.error("Failed to start SNMP pollers: #{inspect(error)}")
+          end
         end)
       end
 

lib/towerops/snmp/poller_worker.ex

@@ -86,10 +86,26 @@ defmodule Towerops.Snmp.PollerWorker do
         now = DateTime.truncate(DateTime.utc_now(), :second)
 
         # Poll all sensors
-        _ = poll_sensors(device.sensors, client_opts, now)
+        try do
+          poll_sensors(device.sensors, client_opts, now)
+          Logger.debug("Polled #{length(device.sensors)} sensors for #{equipment.name}")
+        rescue
+          error ->
+            Logger.error(
+              "Error polling sensors for #{equipment.name}: #{inspect(error)}\n#{Exception.format_stacktrace()}"
+            )
+        end
 
         # Poll all interfaces
-        _ = poll_interfaces(device.interfaces, client_opts, now)
+        try do
+          poll_interfaces(device.interfaces, client_opts, now)
+          Logger.debug("Polled #{length(device.interfaces)} interfaces for #{equipment.name}")
+        rescue
+          error ->
+            Logger.error(
+              "Error polling interfaces for #{equipment.name}: #{inspect(error)}\n#{Exception.format_stacktrace()}"
+            )
+        end
 
         # Schedule next poll
         schedule_next_poll(get_poll_interval(equipment))