Please address the comments from this code review:
## Overall Comments
- In GtkSortTypeFromStr, add an assertion or null-pointer check for outType before dereferencing to avoid potential segfaults if someone passes nullptr.
- Reordering the creation of ProgramData/UiCoreThread before init_theme and logSystem may introduce startup races—ensure the core thread isn’t accessing uninitialized resources.
- Wrap the `-fsanitize=undefined` flags behind a compiler capability check in meson.build to prevent build failures on toolchains that don’t support undefined behavior sanitizer.

## Individual Comments

### Comment 1
<location> `src/iptux/UiModels.cpp:358` </location>
<code_context>
 };

-GtkSortType GtkSortTypeFromStr(const std::string& s) {
+bool GtkSortTypeFromStr(const std::string& s, GtkSortType* outType) {
   for (int i = GTK_SORT_ASCENDING; i <= GTK_SORT_DESCENDING; ++i) {
     if (s == gtk_sort_type_names[i]) {
</code_context>

<issue_to_address>
Consider validating the outType pointer before dereferencing.

Dereferencing a nullptr outType will cause undefined behavior. Please add a check for nullptr and return false if detected.
</issue_to_address>

<suggested_fix>
<<<<<<< SEARCH
bool GtkSortTypeFromStr(const std::string& s, GtkSortType* outType) {
  for (int i = GTK_SORT_ASCENDING; i <= GTK_SORT_DESCENDING; ++i) {
    if (s == gtk_sort_type_names[i]) {
      *outType = (GtkSortType)i;
      return true;
    }
  }
  return false;
}
=======
bool GtkSortTypeFromStr(const std::string& s, GtkSortType* outType) {
  if (!outType) {
    return false;
  }
  for (int i = GTK_SORT_ASCENDING; i <= GTK_SORT_DESCENDING; ++i) {
    if (s == gtk_sort_type_names[i]) {
      *outType = (GtkSortType)i;
      return true;
    }
  }
  return false;
}
>>>>>>> REPLACE

</suggested_fix>

### Comment 2
<location> `src/iptux-core/TransFileModel.cpp:111` </location>
<code_context>
 }

 double TransFileModel::getProgress() const {
+  if (fileLength <= 0) {
+    return 0.0;  // Avoid division by zero
+  }
   return percent(finishedLength, fileLength);
</code_context>

<issue_to_address>
Returning 0.0 for non-positive fileLength may mask input errors.

Consider logging a warning if fileLength is negative, as this may signal a logic error.
</issue_to_address>