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>

compose.yaml

@@ -9,7 +9,6 @@ include:
   - joplin/compose.yaml
   - drop/compose.yaml
   - ai/compose.yaml
-  - asciinema/compose.yaml
   - restic/compose.yaml
   - netdata/compose.yaml
   - umami/compose.yaml