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.

docs/architecture/10-interaction-and-feedback.md

@@ -43,6 +43,28 @@ nature of the message, not by convenience.
   consent-for-destruction in a toast.
 - **Errors persist; success fades.** An error/warning toast waits for the user (a critical
   message must not vanish on a timer); success/info auto-dismiss (~6s).
+- **Toasts sit bottom-right**, not top-right. Carbon's default is the top, but our header's
+  action cluster (Publish/Revert, theme/datasets) lives top-right — a toast there covers the
+  control the user just used. Bottom-anchored, the stack grows upward with the newest toast
+  nearest the corner, and still clears the centered confirm dialog. (`Toaster.module.css`.)
+- **Toast copy: title states it, message adds to it.** Every toast renders a `title` and a
+  `message`. The title is the short headline — the action or what stopped, **no terminal
+  period** ("Snippet published", "Storage full"). The message is **one short sentence that
+  must not paraphrase the title** (Carbon, `components/notification/usage.mdx` §Body
+  content: _"Don't repeat or paraphrase the title"_); it carries the **consequence** for a
+  success ("Your draft is now the published version") or the **next step** for a fixable
+  error. Name the specific item in the message when toasts can stack — a delete confirms
+  _which_ one went ("…removed `\"Sales\"`…").
+- **Toast only what the user can't already see.** A success toast is for an outcome with no
+  strong on-screen cue: a **side effect** (Extract creates a dataset off-screen while the
+  user is in the editor), a **disappearance** (delete), or a **state flip** (publish/revert).
+  An action whose result is immediately visible — a created snippet opening in the editor, a
+  new dataset shown selected — is confirmed by that visible change; adding a toast is noise
+  (NN/g aesthetic-and-minimalist; Carbon `notification/usage.mdx` "Deciding what to use").
+  An **invisible** outcome that still shouldn't toast is **copy-to-clipboard**: confirm it
+  _inline on the control_ ("Copied") with a polite `aria-live` announcement for assistive
+  tech, never a toast-per-copy. This refines the spec's earlier blanket "every action
+  toasts" (spec §01F/§02/§05, reconciled).
 - **The same failure can light up two channels.** An unrenderable spec shows the _same_
   message inline in both the editor (§03E) and the preview (§04) — one producer
   (`PreviewStore`), two subscribers. That's intentional, not duplication.