fix check skip log noise and browser session crash (#87)

- Downgrade check executor skip log from info to debug to stop flooding
  production logs every 60s for every agent-assigned device check
- Fix KeyError on session.user_agent in settings page - BrowserSession
  schema has device_type field, not user_agent

Reviewed-on: graham/towerops-web#87

lib/towerops/workers/check_executor_worker.ex

@@ -58,7 +58,7 @@ defmodule Towerops.Workers.CheckExecutorWorker do
 
   defp execute_or_skip(check) do
     if should_skip_check?(check) do
-      Logger.info("Skipping check #{check.id} (#{check.check_type}) - device has agent or Phoenix SNMP disabled")
+      Logger.debug("Skipping check #{check.id} (#{check.check_type}) - device has agent or Phoenix SNMP disabled")
     else
       execute_and_record(check)
     end

lib/towerops_web/live/user_settings_live.html.heex

@@ -898,7 +898,7 @@
                 <li class="flex items-center justify-between gap-x-6 py-5">
                   <div class="flex items-start gap-x-3 min-w-0 flex-1">
                     <div class="flex-shrink-0 mt-1">
-                      <%= if String.contains?(String.downcase(session.user_agent || ""), ["mobile", "android", "iphone", "ipad"]) do %>
+                      <%= if session.device_type in ["mobile", "tablet"] do %>
                         <.icon name="hero-device-phone-mobile" class="h-6 w-6 text-gray-400" />
                       <% else %>
                         <.icon name="hero-computer-desktop" class="h-6 w-6 text-gray-400" />