feat: move asciinema to dev stack under asciinema.dev.pivoine.art

- Moved asciinema service from standalone stack to dev/compose.yaml
- Updated hostname from asciinema.pivoine.art to asciinema.dev.pivoine.art
- Updated environment variables to use DEV_ASCIINEMA_ prefix
- Updated restic backup volume reference (asciinema_data -> dev_asciinema_data)
- Moved custom.exs to dev/asciinema-custom.exs
- Removed standalone asciinema/compose.yaml directory
- Container name changes from asciinema_app to dev_asciinema
- Volume name changes from asciinema_data to dev_asciinema_data
- Preserved admin interface at admin.asciinema.dev.pivoine.art with Basic Auth

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

restic/compose.yaml

@@ -144,7 +144,7 @@ volumes:
     name: ai_crawl4ai_data
     external: true
   backup_asciinema_data:
-    name: asciinema_data
+    name: dev_asciinema_data
     external: true
   backup_dev_gitea_data:
     name: dev_gitea_data