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/stores/ExtractStore.ts

@@ -17,6 +17,7 @@ import type { DataFormat } from '@core/format-detection';
 import { createDataset } from '@core/dataset';
 import { isNameTaken } from '@core/naming';
 import { useDatasetStore } from './DatasetStore';
+import { notify } from './NotificationStore';
 import { useSnippetStore } from './SnippetStore';
 
 /** The inline `data` block of a parsed spec, if it carries `values`. */
@@ -123,8 +124,14 @@ export const useExtractStore = create<ExtractState>((set, get) => ({
     spec.data = { name };
     useSnippetStore.getState().replaceActiveDraft(JSON.stringify(spec, null, 2), now);
 
-    // TODO (M6, spec §03F): success toast "Dataset created" — deferred with the
-    // other success toasts (see SnippetStore publish/revert breadcrumbs).
+    // Success confirmation (spec §03F). Title states the action; the message
+    // adds the consequence — the spec was rewritten to reference the new dataset
+    // by name (council toast-copy rule, docs/architecture/10 → Toast copy).
+    notify({
+      kind: 'success',
+      title: 'Dataset created',
+      message: `The spec now references "${name}" instead of its inline data.`,
+    });
     set(INITIAL);
     return true;
   },