fix: settings-hook remove exits 1 when nothing to remove

gstack-settings-hook remove was exiting 0 when settings.json didn't
exist, causing gstack-uninstall to report "SessionStart hook" as
removed on clean systems where nothing was installed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bin/gstack-settings-hook

@@ -54,7 +54,7 @@ case "$ACTION" in
     " 2>/dev/null
     ;;
   remove)
-    [ -f "$SETTINGS_FILE" ] || exit 0
+    [ -f "$SETTINGS_FILE" ] || exit 1
     GSTACK_SETTINGS_PATH="$SETTINGS_FILE" bun -e "
       const fs = require('fs');
       const settingsPath = process.env.GSTACK_SETTINGS_PATH;