Fix dataset-ref walk false positive and wire spec-mandated success toasts

- Prune the data payload and top-level datasets keys in all three ref walks
  (extractDatasetRefs, renameDatasetInSpec, resolveDatasetRefs) so a data row
  carrying a field named "data" is no longer misread as a library reference,
  spuriously rewritten, or made to throw DatasetNotFoundError. Adds tests,
  including a guard that lookup-transform refs (from.data) still resolve.
- Wire the deferred success toasts now the Toaster has landed: publish, revert,
  extract-to-dataset, and snippet/dataset delete. Copy follows the council
  title-vs-message rule (title states the action, message adds the consequence).
- Reconcile the spec's blanket toast mandate to "toast only what the user can't
  already see": no toast on visible-result creates (snippet, dataset form);
  Copy Reference stays inline and gains an aria-live announcement (new shared
  .visually-hidden utility) instead of a toast-per-copy.
- Move the toast region to bottom-right so it stops covering the header action
  cluster (Publish/Revert, theme/datasets).
- Update docs/spec 01F/02/05 and docs/architecture/07 + 10 to match.

src/app/components/Toaster.module.css

@@ -1,10 +1,14 @@
 .region {
   position: fixed;
-  top: var(--space-5);
+  /* Bottom-right, not top-right: the header's action cluster (Publish/Revert,
+     theme/datasets controls) lives top-right, and a toast there lands on top of
+     the control the user just used. Bottom-anchored, the stack grows upward and
+     the newest toast sits nearest the corner (docs/architecture/10 → Toasts). */
+  bottom: var(--space-5);
   right: var(--space-5);
   /* Above the confirm backdrop (z 1000) so a failure stays visible and
-     dismissible even with a confirmation open; top-right won't block the
-     centered dialog. */
+     dismissible even with a confirmation open; the corner clears the centered
+     dialog. */
   z-index: 1100;
   display: flex;
   flex-direction: column;