i18n complete: all 16 components translated (CZ/HE/RU/UA)

- Custom i18n provider with React Context + localStorage
- Hebrew RTL support (dir=rtl on html)
- All pages + components use t() calls
- FullCalendar + dates locale-aware
- Language selector in Settings wired to context

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

api/package.json

@@ -17,6 +17,7 @@
     "@fastify/cors": "^11.2.0",
     "@fastify/helmet": "^13.0.2",
     "@fastify/jwt": "^10.0.0",
+    "@fastify/rate-limit": "^10.3.0",
     "@fastify/swagger": "^9.7.0",
     "@fastify/swagger-ui": "^5.2.5",
     "bcrypt": "^6.0.0",