feat: add Supabase auth config to production Docker setup

- Pass SUPABASE_JWT_SECRET to backend in docker-compose.prod.yml
- Add build args (VITE_API_URL, VITE_SUPABASE_URL, VITE_SUPABASE_ANON_KEY)
  to Dockerfile.prod so Vite inlines them at build time
- Pass build args from secrets in deploy workflow
- Add build section to frontend service in docker-compose.prod.yml

No GoTrue container needed in prod — Supabase Cloud hosts the auth
service. The backend only needs the JWT secret to verify tokens.

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

docker-compose.prod.yml

@@ -6,6 +6,7 @@ services:
     environment:
       - DEBUG=false
       - DATABASE_URL=postgresql://postgres:${POSTGRES_PASSWORD}@db:5432/nuzlocke
+      - SUPABASE_JWT_SECRET=${SUPABASE_JWT_SECRET}
     depends_on:
       db:
         condition: service_healthy
@@ -13,6 +14,13 @@ services:
 
   frontend:
     image: gitea.nerdboden.de/thefurya/nuzlocke-tracker-frontend:latest
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile.prod
+      args:
+        - VITE_API_URL=${VITE_API_URL}
+        - VITE_SUPABASE_URL=${VITE_SUPABASE_URL}
+        - VITE_SUPABASE_ANON_KEY=${VITE_SUPABASE_ANON_KEY}
     ports:
       - "9080:80"
     depends_on: