feat(docker): protect production database with external volume

- Mark postgres_data_prod as external volume (slc_postgres_prod_data)
- External volumes are NOT deleted by 'docker compose down -v'
- Add volume creation step to production deployment guide
- Document volume safety measures and dangerous commands
- Add shell alias examples for safe volume management
- Update security checklist with volume creation requirement

Protection: Production database now requires manual volume deletion,
preventing accidental data loss during container management.

docs/DEPLOYMENT.md

@@ -88,7 +88,16 @@ Edit `backend/.env.production`:
 - Add AWS SES credentials
 - Set production `CORS_ORIGIN`
 
-4. **Build production images**
+4. **Create production database volume**
+```bash
+# IMPORTANT: Create external volume before first production start
+# This protects the database from accidental deletion with 'docker compose down -v'
+docker volume create slc_postgres_prod_data
+```
+
+This external volume will NOT be deleted even with `docker compose down -v`.
+
+5. **Build production images**
 ```bash
 docker compose --profile prod build
 ```
@@ -269,6 +278,89 @@ cat backups/backup_YYYYMMDD_HHMMSS.sql | docker exec -i spotlightcam-db psql -U
 
 ---
 
+## Volume Safety & Data Protection
+
+### Production Database Volume Protection
+
+The production database uses an **external volume** (`slc_postgres_prod_data`) that is protected from accidental deletion:
+
+```yaml
+volumes:
+  postgres_data_prod:
+    external: true
+    name: slc_postgres_prod_data
+```
+
+**Key Safety Features:**
+- ✅ **NOT deleted** by `docker compose down`
+- ✅ **NOT deleted** by `docker compose down -v` (even with volumes flag!)
+- ✅ **Survives** container recreation and rebuilds
+- ⚠️ Must be manually created before first production deployment
+
+**Volume Commands:**
+```bash
+# Create volume (before first deployment)
+docker volume create slc_postgres_prod_data
+
+# List volumes
+docker volume ls
+
+# Inspect volume
+docker volume inspect slc_postgres_prod_data
+
+# Manual deletion (if absolutely necessary)
+docker volume rm slc_postgres_prod_data  # Requires manual confirmation
+```
+
+### Safe vs Dangerous Commands
+
+**SAFE - Will NOT delete data:**
+```bash
+docker compose down                      # Removes containers only
+docker compose --profile prod down       # Removes prod containers only
+docker compose restart                   # Restart containers
+docker compose up --build                # Rebuild and restart
+```
+
+**DANGEROUS - Could delete development data:**
+```bash
+docker compose down -v                   # Deletes dev volumes (postgres_data)
+docker compose down --volumes            # Same as above
+```
+
+**PROTECTED - Production database is safe even with:**
+```bash
+docker compose --profile prod down -v    # prod volume is EXTERNAL, won't be deleted
+```
+
+### Additional Safety Measures
+
+**1. Shell Aliases (add to ~/.bashrc or ~/.zshrc):**
+```bash
+# Safe shutdown
+alias dcd='echo "✅ docker compose down - volumes SAFE"; docker compose down'
+
+# Dangerous shutdown with confirmation
+alias dcdv='echo "🚨 WARNING! docker compose down -v DELETES VOLUMES!"; \
+  echo "Type YES to continue:"; read response; \
+  [ "$response" = "YES" ] && docker compose down -v || echo "❌ Cancelled"'
+```
+
+**2. Regular Backups:**
+Always maintain automated backups regardless of volume protection:
+```bash
+# Daily backup at 2 AM
+0 2 * * * docker compose exec db-prod pg_dump -U spotlightcam spotlightcam | gzip > /backups/db-$(date +\%Y\%m\%d).sql.gz
+```
+
+**3. Pre-deployment Checklist:**
+- [ ] Production volume created: `docker volume ls | grep slc_postgres_prod_data`
+- [ ] Volume is marked as external in docker-compose.yml
+- [ ] Backup script is configured and tested
+- [ ] Team knows NOT to use `-v` flag on production
+
+---
+
 ## Monitoring & Logging
 
 ### View logs
@@ -312,6 +404,7 @@ Logs are configured with rotation:
 
 ### Before Going to Production
 
+- [ ] **Create external database volume:** `docker volume create slc_postgres_prod_data`
 - [ ] Generate strong JWT secret (64+ characters)
 - [ ] Use strong database password (20+ characters)
 - [ ] Configure AWS SES in production mode (not sandbox)