Guarded tree view palette application to use GTK3 font descriptions or GTK2 styles appropriately.
Adjusted the chanview creation call site to pass GTK3 font descriptions or GTK2 styles based on the build.
Switched channel tree and theme application logic to use the new palette helper.
Updated entry and user list styling to route palette/font application through the helper.
Applied gtk_box_set_homogeneous() in GTK3 branches where the GTK2 code requested homogeneous layout (e.g., dialog hboxes).
Updated remaining helpers and setup/preferences UI box constructors (including the shared mg_box_new helper) to follow the same GTK3/GTK2 branching approach consistently across src/fe-gtk/
- Replaced the dark mode checkbox with an Auto/Dark/Light color mode selector and ensured palette edits use the resolved mode.
- Applied the resolved color mode consistently across palette saving and GTK styling in the user list and channel tree/theme application paths.
- Removes need to check for malloc failure
- Removes need for NULL checks on free
- Adds checks for integer overflows
- Removes some extra memset calls
- Removes chance of mixing libc and glib malloc/free
