fix(defaults): treat a read-denied defaults file as invalid

NestDefaults.Load caught only JsonException and IOException, so a
defaults.json that File.Exists can see but the process cannot read
threw UnauthorizedAccessException out of New. Report such files as
Invalid and return the fallback values, like a corrupt file.

The regression mode-000s the file on Unix (skipped on Windows and when
running as root); it failed with UnauthorizedAccessException before
this change.

OpenNest.Data/NestDefaults.cs

@@ -88,13 +88,10 @@ public sealed class NestDefaults
             var json = File.ReadAllText(path);
             dto = JsonSerializer.Deserialize<NestDefaultsDto>(json, JsonOptions);
         }
-        catch (JsonException)
-        {
-            status = NestDefaultsStatus.Invalid;
-            return defaults;
-        }
-        catch (IOException)
+        catch (Exception ex) when (IsUnreadableFile(ex))
         {
+            // A file that exists but cannot be read (locked, access-denied)
+            // or parsed must never block creating a nest.
             status = NestDefaultsStatus.Invalid;
             return defaults;
         }
@@ -228,6 +225,14 @@ public sealed class NestDefaults
         }
     }
 
+    private static bool IsUnreadableFile(Exception ex) =>
+        ex
+            is JsonException
+                or IOException
+                or UnauthorizedAccessException
+                or NotSupportedException
+                or System.Security.SecurityException;
+
     private static bool IsValidSize(double width, double length) =>
         !double.IsNaN(width)
             && !double.IsNaN(length)