ZOITECHAT_ICON_PATH (user override env var),
current working directory + share/icons,
argv[0] directory + share/icons.
Valid directories are appended to GTK’s icon search path.
Added diagnostic logging so startup clearly reports either the selected icon path source/path or that none of the expected locations were usable, to speed up Windows missing-icon triage.
Reused/stored the computed argv[0] directory in fe_args (via win32_argv0_dir) so it can be used both for chdir and for icon fallback resolution.