Removed GTK2 compatibility shims from headers (fe-gtk.h, gtkutil.h), leaving direct GTK3-facing declarations/includes only (and platform-specific guards unrelated to GTK2 kept as-is).
Cleaned GTK2-specific comments/wording now that behavior is GTK3-native (menu accelerator note and emoji/userlist comment blocks).
Updated GTK3-specific palette color storage handling in DCC, notify, and user list views to align with HAVE_GTK3 guards.
Standardized setup color application and dialog logic to use HAVE_GTK3 branches for GTK3/GTK2 separation.
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.
- 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.
