chore: groundwork for media purge system

docs/design/components.md

@@ -814,3 +814,18 @@ Exact values live in `source/AppFrame.dc.html` (the Settings and Home states). C
 | RestartOverlay | custom full-page `role="status"` | title, text, startedAt, slow | reload | App shell |
 | UpdateBanner | UAlert | state: 'available'\|'ready' | go-to-settings, dismiss | Home (owner) |
 | UpdatePill | UBadge | none | none | DashboardShell Settings item (dot on mobile) |
+
+## Added with Media cleanup
+### PurgeDuplicatesDialog
+Used by Settings ("Purge now") and Media, Duplicates tab ("Purge duplicates"). Built on `UModal`, `sm:max-w-md`, bottom sheet on mobile, cancel first, confirm is `color="error"`.
+- Props: `open`, `preview` (`groups`, `copies`, `articles`, `list[]`, `more`), `status` (`loading | ready | purging | nothing | error | partial | conflict`).
+- While `purging`: confirm shows `loader-circle` and reads "Purging…"; `dismissible` false, Cancel disabled.
+- Group row: 40×30 thumbnail, filename, "Kept · used in N articles", right-aligned "N copies merged". Max 5 rows, then "and N more groups".
+- Notices sit above the summary in a `UAlert` (soft): error for failure, warning for partial and conflict.
+- Emits `purged` (with counts). The parent shows the toast.
+
+### MediaCleanupCard
+Settings card. `USwitch` (square, `rounded-none`), `UInputNumber` with "days" suffix, read-only lines, divider, outline button. Saves on change and on blur or Enter; shows "Saving…" then "Saved" in the header. Read-only mode disables controls, hides the button and shows an info `UAlert`.
+
+### Media toolbar button
+Secondary `UButton` icon `merge`, label "Purge duplicates", after the sort menu on desktop; full width in the stacked toolbar on mobile (44 px).