docs(rollback): Add quick reference guide

apps/demo-nginx/docs/ROLLBACK_QUICK_REF.md

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+# 🔄 Manual Rollback - Quick Reference
+
+## 🚀 Quick Start (2 minutes)
+
+```
+Jenkins → demo-nginx-rollback → Build with Parameters
+
+ROLLBACK_METHOD: IMAGE_TAG
+TARGET_VERSION: main-21
+SKIP_HEALTH_CHECK: true (recommended!)
+DRY_RUN: false
+
+→ Build → ✅ SUCCESS!
+```
+
+---
+
+## 📋 3 Ways to Rollback
+
+### 1. By Image Tag (Fastest)
+```
+Method: IMAGE_TAG
+Target: main-21
+Use: When you know the build number
+```
+
+### 2. By Revision Number
+```
+Method: REVISION_NUMBER
+Target: 2
+Use: Rollback N steps back
+Find: kubectl rollout history deployment/demo-nginx -n demo-app
+```
+
+### 3. By Git Commit
+```
+Method: GIT_COMMIT
+Target: abc123def
+Use: Exact code state
+Find: git log --oneline apps/demo-nginx/deployment.yaml
+```
+
+---
+
+## ⚡ Emergency Rollback (30 seconds)
+
+```bash
+# Fastest - kubectl
+kubectl rollout undo deployment/demo-nginx -n demo-app
+
+# To specific revision
+kubectl rollout undo deployment/demo-nginx -n demo-app --to-revision=25
+```
+
+---
+
+## 🔍 Verify Rollback
+
+```bash
+# Check image
+kubectl get deployment demo-nginx -n demo-app \
+  -o jsonpath='{.spec.template.spec.containers[0].image}'
+
+# Check pods
+kubectl get pods -n demo-app -l app=demo-nginx
+
+# Test health
+POD=$(kubectl get pods -n demo-app -l app=demo-nginx -o jsonpath='{.items[0].metadata.name}')
+kubectl exec $POD -n demo-app -- wget -q -O- http://localhost/health
+```
+
+---
+
+## ⚙️ Parameters
+
+| Parameter | Default | Recommended |
+|-----------|---------|-------------|
+| ROLLBACK_METHOD | IMAGE_TAG | IMAGE_TAG |
+| TARGET_VERSION | (required) | main-21 |
+| SKIP_HEALTH_CHECK | false | **true** |
+| DRY_RUN | false | false |
+
+---
+
+## 🐛 Common Issues - FIXED
+
+| Issue | Fix | Status |
+|-------|-----|--------|
+| Wrong container name | Use `nginx` | ✅ Fixed |
+| Whitespace in input | Auto-trim | ✅ Fixed |
+| RBAC permission | Added pods/exec | ✅ Fixed |
+| Health check timing | Use SKIP_HEALTH_CHECK | ⚠️ Workaround |
+| Bash loop broken | Use `1 2 3 4 5` | ✅ Fixed |
+
+---
+
+## 💡 Best Practices
+
+1. ✅ Always test with `DRY_RUN: true` first
+2. ✅ Use `SKIP_HEALTH_CHECK: true` for faster rollback
+3. ✅ Verify manually after rollback (30-60s wait)
+4. ✅ Document rollback reason in Jenkins build comment
+5. ✅ Check ArgoCD sync status after rollback
+
+---
+
+## 📊 Verification Commands
+
+```bash
+# Full status check
+kubectl get deployment demo-nginx -n demo-app
+kubectl get pods -n demo-app -l app=demo-nginx
+kubectl rollout history deployment/demo-nginx -n demo-app
+
+# Watch pods update
+watch kubectl get pods -n demo-app
+
+# Check logs
+kubectl logs -n demo-app -l app=demo-nginx --tail=50
+```
+
+---
+
+## 🎯 Success Checklist
+
+- [ ] Jenkins pipeline exists (demo-nginx-rollback)
+- [ ] RBAC configured (pods/exec permission)
+- [ ] Target version identified
+- [ ] DRY_RUN tested
+- [ ] Rollback executed
+- [ ] Pods verified (Running)
+- [ ] Image version confirmed
+- [ ] Health check passed (manual)
+- [ ] ArgoCD synced
+
+---
+
+## 📚 Full Documentation
+
+See: [apps/demo-nginx/docs/ROLLBACK_MANUAL.md](./ROLLBACK_MANUAL.md)
+
+---
+
+**Quick Reference - Keep this handy! 📌**