fix: infer device role during discovery and handle string price values

Device Type Fix:
- Add Topology.maybe_update_device_role() call after discovery completes
- Device types (AP, router, switch, etc.) now inferred immediately after discovery
- Previously devices showed 'unknown' until first polling cycle completed
- Role inference uses SNMP manufacturer, model, and system description

Billing Fix:
- Handle string values from Settings.get_setting() in default_price_per_device()
- Add case clause to convert string '2.00' to Decimal struct
- Fixes CaseClauseError crash on /orgs/:slug/settings page

All discovery tests passing.

lib/towerops/billing.ex

@@ -39,6 +39,7 @@ defmodule Towerops.Billing do
     case Settings.get_setting("default_price_per_device") do
       nil -> @default_price_per_device
       %Decimal{} = decimal -> decimal
+      string when is_binary(string) -> Decimal.new(string)
     end
   end
 

lib/towerops/snmp/discovery.ex

@@ -33,6 +33,7 @@ defmodule Towerops.Snmp.Discovery do
   alias Towerops.Snmp.Sensor
   alias Towerops.Snmp.Storage
   alias Towerops.Snmp.Vlan
+  alias Towerops.Topology
   alias Towerops.Workers.DiscoveryWorker
 
   require Logger
@@ -276,6 +277,10 @@ defmodule Towerops.Snmp.Discovery do
           {:ok, check_counts} = Towerops.Snmp.create_checks_from_discovery(device, discovered_device)
           log_check_creation_results(device.id, check_counts)
 
+          # Infer and update device role from SNMP data
+          Logger.info("Inferring device role...", device_id: device.id)
+          _ = Topology.maybe_update_device_role(device)
+
           _ =
             Phoenix.PubSub.broadcast(
               Towerops.PubSub,