refactor : reorganize infra files into infra/dev and infra/prod

Consolidate Docker, Nginx, and deploy configs from 5 scattered directories
(docker/, deploy/docker/, deploy/nginx/, script/) into a single infra/ tree
with dev/ and prod/ subdirectories. Update all references in docker-compose,
Makefile, CI workflows, Dockerfiles, and documentation.

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

.dockerignore

@@ -2,10 +2,11 @@
 .gitea
 .env.local
 .env.test
-docker/
-deploy/docker/docker-compose.prod.yml
-deploy/docker/deploy.sh
-deploy/docker/.env.example
+infra/dev/
+infra/prod/docker-compose.yml
+infra/prod/deploy.sh
+infra/prod/deploy-release.sh
+infra/prod/.env.example
 frontend/node_modules
 frontend/.nuxt
 frontend/.output