[Plugin request] Archival

- [ ] Zites, when created, receives a .git subfolder, that turns it into empty repos
- [ ] Zite owner can commit directly from Sidebar
- [ ] Option on Sidebar to turn current zite into an archivable
- [ ] When accessing zite, user receives a notification, if wants to archive it
- [ ] When disk is nearly full, user receives notification

No files, tests, or entry points are identified in the issue. Start by mapping each checklist item to the relevant plugin, Sidebar, notification, storage, and repository code, then clarify the expected archival workflow and disk-full behavior. Done means all five listed capabilities are implemented with tests covering creation, commits, archiving prompts, and low-disk notifications.

索引モデルが issue の本文から書いたものです。