PM2 cluster deploy + Redis caching + Nginx gzip + UI polish

- PM2 v6: 2x API cluster + 1x web, zero-downtime reload
- Redis cache: 30s TTL on GET /tasks, X-Cache header
- Nginx gzip compression
- Mobile touch targets 44px
- Czech diacritics throughout UI
- TaskModal slide-up animation
- StatusBadge color dots
- GroupSelector emoji icons

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/package.json

@@ -22,6 +22,7 @@
     "bcrypt": "^6.0.0",
     "dotenv": "^17.3.1",
     "fastify": "^5.8.4",
+    "ioredis": "^5.10.1",
     "pg": "^8.20.0",
     "redis": "^5.11.0",
     "uuid": "^13.0.0"