feat: Add multi-agent-guide skill and update reference-curator configs

- Add 91-multi-agent-guide skill for setting up multi-agent collaboration
  with templates for AGENTS.md, Claude, Gemini, Codex configs, and CI/CD
- Add USER-GUIDE.md for reference-curator documentation
- Update default paths in reference-curator configs to use
  ~/Documents/05_AI Agent/10_Reference Library/
- Update settings-audit-report.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

custom-skills/91-multi-agent-guide/.claude-plugin/plugin.json

@@ -0,0 +1,18 @@
+{
+  "name": "multi-agent-guide",
+  "version": "1.0.0",
+  "description": "Multi-agent collaboration framework for complex projects. Sets up agent hierarchies, ownership rules, guardrails, handoff protocols, and CI/CD integration for Claude, Gemini, Codex, and Human agents working together.",
+  "author": {
+    "name": "OurDigital",
+    "email": "ourdigital@example.com"
+  },
+  "keywords": [
+    "multi-agent",
+    "collaboration",
+    "guardrails",
+    "ownership",
+    "ci-cd",
+    "project-management"
+  ],
+  "license": "MIT"
+}