Removed an old commented-out gtk_container_set_border_width(...) line that was dead/commented code in cv_tabs_init.
Simplified the tab-switch condition by removing a legacy commented expression from if (is_switching).
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 multiple GTK UI layout paths (setup, server list, notify, ban list, join dialog, and menu) to use the new helpers for GTK3-safe box/grid creation and attachment behavior.
Added GTK3-safe attach option definitions and updated helper signatures to avoid GTK2-only types/macros in public headers.
Updated gtkutil grid-attachment helpers to use the new attach option type in alignment/expansion logic.
Switched banlist grid attachments to the new helper option flags for GTK3 builds.
Updated GTK helper usages to reference the new ICON_* (and label) macros so GTK3 builds no longer pass stock IDs to button/icon helpers or dialogs, including banlist buttons, DCC windows, rawlog actions, notify dialog/buttons, pevent dialog buttons, tray menu items, and join dialog image helper usage.
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/
