The grep -v alternation in the git-enhanced two-way merge step was missing
the 'gsd-update' arm after the slash-command rename from /gsd:update to
/gsd-update. Commits authored by the current update flow fell through the
filter and were misclassified as user customizations, causing spurious merge
prompts during /gsd-update --reapply.
Adds 'gsd-update' between 'gsd:update' and 'GSD update'. The legacy
'gsd:update' arm is preserved for back-compat; 'GSD update' and 'gsd-install'
exclusions are unchanged.