feat(apply): per-record selection + deletes-before-updates ordering

RecordDiff.Key() gives a stable normalized identifier ("TYPE name.") for
every diff kind, exposed as recordView.Key. ApplyRequest now takes
Updates/Prunes key lists instead of two booleans, so callers can apply a
subset of records. service.Apply builds the applied set with selected
prunes (Delete) added before selected updates (Add/Update) — an
invariant, not an option — since the provider rejects an Add/Update
whose name still conflicts with an existing record (e.g. a CNAME cannot
be created while an A on the same name still exists).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwxdSt4reTm7Dj1oxRvpP3

internal/api/handlers.go

@@ -66,15 +66,16 @@ func (a *API) handleApply(w http.ResponseWriter, r *http.Request) {
 	var req applyRequest
 	if r.Body != nil {
 		r.Body = http.MaxBytesReader(w, r.Body, 1<<20) // 1 MiB
-		// пустое тело допустимо → значения по умолчанию (prune=false);
-		// любая другая ошибка decode (битый JSON, неверные типы) → 400
+		// пустое тело допустимо → значения по умолчанию (пустые списки, ничего
+		// не применяется); любая другая ошибка decode (битый JSON, неверные
+		// типы) → 400
 		if err := json.NewDecoder(r.Body).Decode(&req); err != nil && !errors.Is(err, io.EOF) {
 			writeErr(w, http.StatusBadRequest, "invalid request body")
 			return
 		}
 	}
 	cs, err := a.Svc.Apply(r.Context(), pid, did, service.ApplyRequest{
-		ApplyUpdates: req.ApplyUpdates, ApplyPrunes: req.ApplyPrunes,
+		Updates: req.Updates, Prunes: req.Prunes,
 	})
 	if err != nil {
 		log.Printf("api: apply failed: %v", err)