Updated setup color selection and styling to use RGBA-aware GTK3 overrides/CSS while preserving GTK2 behavior in guarded paths.
Switched tree view color models/renderers and other palette consumers (user list, notify, DCC, menus, spell entry, input style) to RGBA-aware types/properties with shared RGB16 conversion usage.
- 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.
- Updated xtext palette APIs to accept internal color arrays directly for rendering setup.
- Wired xtext palette creation through UI entry points to use the new palette helper when constructing or refreshing text views.
- 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
