chore: remove ruflo and frontend-design — full cleanup

Both plugins removed from all config, scripts, and documentation:
- ruflo: uninstalled globally (npm), removed from install/update/doctor/session-start/detect/lock/advisor
- frontend-design: removed from install/session-start/detect/advisor (was already commented out)
- plugin-advisor.md: compatibility matrix, decision table, conditional rules, recommended sets all updated
- README.md/USAGE.md: all references cleaned, token cost estimates recalculated
- install-plugins.sh: steps renumbered (10→9 steps)
- CHANGELOG.md: kept as historical record

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hooks/session-start.sh

@@ -48,11 +48,10 @@ unset _lib
 TOGGLE_ACTIVE=()
 TOGGLE_INACTIVE=()
 
-for plugin in gstack uiux_pro_max frontend_design plugin_dev context7 ruflo graphifyy; do
+for plugin in gstack uiux_pro_max plugin_dev context7 graphifyy; do
   # Map function name to display name
   case "$plugin" in
     uiux_pro_max)    display="ui-ux-pro-max" ;;
-    frontend_design) display="frontend-design" ;;
     plugin_dev)      display="plugin-dev" ;;
     *)               display="$plugin" ;;
   esac
@@ -104,10 +103,8 @@ detect_superpowers 2>/dev/null && _passive_t=$((_passive_t + 800))
 declare -A _plugin_costs=(
   [gstack]=2750
   [ui-ux-pro-max]=400
-  [frontend-design]=200
   [plugin-dev]=100
   [context7]=200
-  [ruflo]=1000
   [graphifyy]=300
 )
 for _p in "${TOGGLE_ACTIVE[@]}"; do