fix: handle nil sys_descr in profile matching

Fixes FunctionClauseError when sys_descr is nil during device profile
matching. Added nil check before attempting String.contains? comparison.

lib/towerops/profiles/yaml_profiles.ex

@@ -783,6 +783,10 @@ defmodule Towerops.Profiles.YamlProfiles do
       patterns == [] and regexes == [] ->
         true
 
+      # sys_descr is nil - cannot match patterns/regexes
+      is_nil(sys_descr) ->
+        false
+
       # Has pattern constraints - must match at least one
       patterns != [] ->
         Enum.any?(patterns, fn pattern -> String.contains?(sys_descr, pattern) end)