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>

lib/detect-plugins.sh

@@ -42,11 +42,6 @@ detect_gsd() {
   command -v gsd &>/dev/null
 }
 
-detect_frontend_design() {
-  local cache_dir="$HOME/.claude/plugins/cache"
-  [ -d "$cache_dir" ] && ls "$cache_dir" 2>/dev/null | grep -qi "frontend-design"
-}
-
 detect_plugin_dev() {
   # plugin-dev replaces the old "skill-creator" reference
   local cache_dir="$HOME/.claude/plugins/cache"
@@ -63,11 +58,6 @@ detect_context7() {
   command -v ctx7 &>/dev/null
 }
 
-detect_ruflo() {
-  # Ruflo CLI — installed globally via npm
-  command -v ruflo &>/dev/null
-}
-
 detect_graphifyy() {
   # Graphifyy — codebase knowledge graph, installed via pipx
   command -v graphify &>/dev/null