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>

plugins.lock.json

@@ -15,11 +15,6 @@
     "managed_by": "git submodule",
     "note": "Version controlled by submodule pointer in .gitmodules. Update: git submodule update --remote"
   },
-  "ruflo": {
-    "source": "npm:ruflo",
-    "version": "3.5.58",
-    "note": "Enterprise multi-agent orchestration CLI (formerly claude-flow). Standalone CLI, not an MCP server. Check latest at https://www.npmjs.com/package/ruflo before updating."
-  },
   "ctx7": {
     "source": "npm:ctx7",
     "version": "latest",