Added/kept lifecycle call sites for main and detached/channel windows, with comments explaining that .zoitechat-dark / .zoitechat-light classes are required for GTK CSS selectors. This includes top/tab windows and server list/edit windows.
Wired dialog/toplevel creation paths in src/fe-gtk/ to call fe_apply_theme_to_toplevel() (without duplicating platform logic), including common prompt/message dialogs and feature-specific dialogs (join, notify, setup, ignore/ban, etc.), each with the requested brief comment near the new call site.
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 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/
