feat: add Docker Compose support for Discord bot deployment

- Add Dockerfile with multi-stage build for picoclaw
- Add docker-compose.discord.yml for Discord bot service
- Add docker-compose.yml for agent mode service
- Add .env.example with environment variable template
- Add .dockerignore for optimized builds
- Update README.md with Docker Compose section and language switch
- Add README.ja.md (Japanese documentation)
- Update .gitignore with Docker-related entries

.dockerignore

@@ -0,0 +1,10 @@
+.git
+.gitignore
+build/
+.picoclaw/
+config/
+.env
+.env.example
+*.md
+LICENSE
+assets/