feat: initial Jimi Gallery prototype

- Public site (Home/Artists/Exhibitions/News/About/Contact) with EN/KO/JA i18n
- Admin panel with login, CRUD, image upload, multilingual editing
- Exhibition slider/lightbox view
- FastAPI + MongoDB backend, JWT auth
- Docker Compose deployment, behind nginx at jimi.yakenator.io

backend/.env.example

@@ -0,0 +1,4 @@
+ADMIN_PASSWORD=admin
+JWT_SECRET=change-me-to-a-long-random-string
+MONGO_URL=mongodb://mongo:27017
+DB_NAME=jimi_gallery