The datasets table is a snapshot explorer, and snapshots can be deleted

Renamed Datasets to Snapshots and turned the columns around to match: how many each
dataset has and what they cost come first, the dataset's own size after. Opening one lists
its snapshots with when it was taken, when it expires — read from the TTL in its own name,
so no server call is needed — its size, and a Delete button. Deleting takes the same-named
snapshot on descendant datasets too, which is how a recursive schedule made it, and says so
before it does anything.

Dropped "What would it delete?" from the schedule cards, and the endpoint behind it. Run
now says plainly that expired snapshots go at the same time, which is the whole of what the
preview was telling anyone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/api/zfs.go

@@ -217,24 +217,6 @@ func (s *Server) zfsPolicy(id string) (storage.Policy, bool) {
 	return storage.Policy{}, false
 }
 
-// zfsPreview is what this schedule would destroy if it ran now. Nothing is deleted.
-func (s *Server) zfsPreview(w http.ResponseWriter, r *http.Request) {
-	p, ok := s.zfsPolicy(r.PathValue("id"))
-	if !ok {
-		jsonErr(w, 404, "no such schedule")
-		return
-	}
-	doomed, err := s.storage.Doomed(r.Context(), &p)
-	if err != nil {
-		jsonErr(w, 500, err.Error())
-		return
-	}
-	if doomed == nil {
-		doomed = []storage.Snapshot{}
-	}
-	jsonOK(w, 200, map[string]any{"expired": doomed})
-}
-
 func (s *Server) zfsRunNow(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
 	p, ok := s.zfsPolicy(id)