feat(workspaces): archive option + archived-workspaces view

Consume the backend's archive contract (feature/archive-workspaces):

- adapter/http: archive(id)/unarchive(id) (PUT/DELETE /workspaces/:id/archive);
  list(archived?) passes the ?archived= query
- logic/view-model: pure applyArchived(list, id, archived)
- store.svelte: setArchived(id, archived) (optimistic + revert-on-error +
  reconciling refresh); archivedList + refreshArchived() for the archived view
- ui/TileActionBar: new Archive action (the right-click→select action bar)
- ui/HomeHeader: new Archived button opens the archived view
- ui/ArchivedWorkspaces (new): modal listing archived workspaces with
  Unarchive + View (navigates to /<id>)
- ui/WorkspacesHome: wire the Archive action + the Archived modal
- .dispatch/wire.reference.md + backend-handoff.md: record the contract delta

1 files changed, 14 insertions, 0 deletions

diff --git a/src/features/workspaces/logic/view-model.ts b/src/features/workspaces/logic/view-model.ts
index 6f5a635..cdf99c8 100644
--- a/src/features/workspaces/logic/view-model.ts
+++ b/src/features/workspaces/logic/view-model.ts
@@ -84,6 +84,20 @@ export function applyStarred<T extends WorkspaceEntry>(
 }
 
 /**
+ * Return a NEW list with the one workspace's `archived` flag set (immutably —
+ * the entry is replaced, the rest keep their identity). Pure: the optimistic
+ * archive/unarchive transformation shared by the apply + the error revert. A
+ * missing `id` leaves the list unchanged; a subsequent refresh reconciles.
+ */
+export function applyArchived<T extends WorkspaceEntry>(
+  workspaces: readonly T[],
+  id: string,
+  archived: boolean,
+): T[] {
+  return workspaces.map((w) => (w.id === id ? { ...w, archived } : w));
+}
+
+/**
  * Format an epoch-ms timestamp as a short relative string ("now", "3m", "2h",
  * "5d", or a date). Pure: `now` + `then` in, string out. Future timestamps
  * (a workspace just created) read as "now".