chore(deploy): Docker production config, nginx gzip/cache, deploy docs

- docker-compose.yml: restart always, env_file, named volume, start_period
- frontend/nginx.conf: gzip compression, cache headers for assets, no-cache for SW
- Makefile: add prod-down and prod-logs targets
- docs/DEPLOY.md: Dokploy + Cloudflare Tunnel deploy instructions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -1,4 +1,4 @@
-.PHONY: dev build up down logs migrate test shell-backend shell-frontend seed backup prod-build prod-up
+.PHONY: dev build up down logs migrate test shell-backend shell-frontend seed backup prod-build prod-up prod-down prod-logs
 
 # Development
 dev:
@@ -43,3 +43,9 @@ prod-build:
 
 prod-up:
 	docker compose up -d
+
+prod-down:
+	docker compose down
+
+prod-logs:
+	docker compose logs -f