Restructure Docker for Dokploy deployment

- Copy app code into PHP image, sync to shared volume at startup
- Use named volume (app_code) shared between app and nginx
- Build nginx image with embedded config (no bind mounts)
- Add .dockerignore to optimize image build
- Build context moved to project root for both services

docker/nginx/Dockerfile

@@ -0,0 +1,2 @@
+FROM nginx:1.25-alpine
+COPY docker/nginx/default.conf /etc/nginx/conf.d/default.conf