fix: strip LibreNMS template variables from sensor OIDs

LibreNMS sensor OIDs contain template variables like '.{{ $index }}'
which need to be removed before performing SNMP walks.

Added clean_oid_template/1 to strip these template variables:
- '.1.3.6.1.4.1.17713.21.2.1.36.{{ $index }}' -> '.1.3.6.1.4.1.17713.21.2.1.36'
- 'sysUptime.{{ $index }}' -> 'sysUptime'

The SNMP walk will now use the base OID and discover all instances
with their actual index values.

lib/towerops/snmp/profiles/dynamic.ex

@@ -104,7 +104,11 @@ defmodule Towerops.Snmp.Profiles.Dynamic do
     oid = sensor_def.num_oid || sensor_def.oid
 
     if oid do
-      case Client.walk(client_opts, oid) do
+      # Remove LibreNMS template variables like ".{{ $index }}" from OID
+      # For walks, we need the base OID without the index placeholder
+      walk_oid = clean_oid_template(oid)
+
+      case Client.walk(client_opts, walk_oid) do
         {:ok, results} when is_list(results) and results != [] ->
           # Convert walk results to sensor data
           Enum.map(results, fn result ->
@@ -112,11 +116,11 @@ defmodule Towerops.Snmp.Profiles.Dynamic do
           end)
 
         {:ok, _empty} ->
-          Logger.debug("No data found for sensor OID: #{oid}")
+          Logger.debug("No data found for sensor OID: #{walk_oid}")
           []
 
         {:error, reason} ->
-          Logger.warning("Failed to walk sensor OID #{oid}: #{inspect(reason)}")
+          Logger.warning("Failed to walk sensor OID #{walk_oid}: #{inspect(reason)}")
           []
       end
     else
@@ -125,6 +129,16 @@ defmodule Towerops.Snmp.Profiles.Dynamic do
     end
   end
 
+  # Remove LibreNMS template variables from OID
+  # Examples:
+  #   ".1.3.6.1.4.1.17713.21.2.1.36.{{ $index }}" -> ".1.3.6.1.4.1.17713.21.2.1.36"
+  #   "sysUptime.{{ $index }}" -> "sysUptime"
+  defp clean_oid_template(oid) do
+    oid
+    |> String.replace(~r/\.?\{\{[^}]+\}\}/, "")
+    |> String.trim_trailing(".")
+  end
+
   defp build_sensor_data(sensor_def, %{oid: oid, value: value}) do
     # Build sensor index from OID (extract last component)
     sensor_index = extract_index_from_oid(oid, sensor_def.index)