Add production Dockerfiles and nginx config

Backend: installs non-editable, runs uvicorn without reload.
Frontend: multi-stage build, serves static files via nginx with
API proxy to the backend service and SPA fallback routing.

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

docker-compose.prod.yml

@@ -1,6 +1,9 @@
 services:
   api:
     image: gitea.nerdboden.de/julian/nuzlocke-tracker-api:latest
+    build:
+      context: ./backend
+      dockerfile: Dockerfile.prod
     command: >
       sh -c "alembic upgrade head && uvicorn app.main:app --host 0.0.0.0 --port 8000 --app-dir src"
     environment:
@@ -13,6 +16,9 @@ services:
 
   frontend:
     image: gitea.nerdboden.de/julian/nuzlocke-tracker-frontend:latest
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile.prod
     ports:
       - "8080:80"
     depends_on: