chore: groundwork for media purge system

docs/design/states.md

@@ -281,3 +281,27 @@ Added by the Media screens, none of which exist yet:
 - `POST /v1/media/merge`: `{ keep_id, merge_ids }`. Rewrites article bodies from the merged copies' URLs to the kept image's URL, then deletes the copies. 200 with `{ articles_updated, merged }`, 404, 409 when a listed copy is gone or the group changed.
 - `GET /v1/media/{id}/usage`: `[{ id, title, published }]`, read from article bodies.
 - Images no longer belong to an article, and deleting an article no longer deletes images. `POST /v1/article/{id}/image` and `DELETE /v1/article/{id}/image/{imageId}` are replaced by the endpoints above.
+
+## Added with Media cleanup
+### Media cleanup
+| State | Surface | Behaviour |
+|---|---|---|
+| Default | Settings card | Off, "Never run", no "Every" row |
+| On | Settings card | "Every" 30 days, last and next run |
+| Saving / Saved | Settings card header | "Saving…" then "Saved" for 2 s, polite live region |
+| Save failed | Under the field | "Couldn't save. Try again in a moment." Control reverts |
+| Validation | Under the field | "Enter a whole number of days between 1 and 365." Nothing sent |
+| Read-only | Settings card | Controls disabled, button hidden, info alert |
+| Loading | Settings card | Skeleton after 150 ms |
+| Offline | Settings and Media | Banner as on Media. Controls and buttons disabled |
+| Preview loading | Dialog | Skeleton rows, confirm disabled |
+| Confirm | Dialog | Summary, up to 5 groups, link to Duplicates |
+| In progress | Dialog | "Purging…", loader-circle, not dismissible |
+| Nothing to purge | Dialog | Info state, "Close" only |
+| Error | Dialog | Notice, stays open, confirm retries |
+| Partial | Dialog | Warning, summary refreshes, "Close" and "Retry" |
+| Conflict (409) | Dialog | Warning, summary refreshes |
+| Success | Toast, 5 s | "Duplicates purged" / "9 copies merged. 12 articles updated." "Last purge" updates in place |
+| Unattended run | Settings | No toast. Updated on next visit |
+
+401 and 403 are global and have no local copy.