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/spec/01-application-shell.md

@@ -99,13 +99,17 @@ Transient toast messages appear in a corner of the screen to confirm actions or
 - Each toast auto-dismisses after a few seconds, and can also be dismissed manually via its close control.
 - Multiple toasts stack rather than replacing one another, and appear/disappear with a brief fade.
 
+Toasts confirm outcomes the user **cannot already see** — a side effect, a disappearance, or a state change with no strong on-screen cue. An action whose result is immediately visible (a newly created snippet opening in the editor; a new dataset shown selected in its detail pane) is confirmed by that visible change, not by an added toast, which would only be noise (Nielsen Norman "aesthetic and minimalist design"; Carbon notification usage; see _docs/architecture/10 → Toast copy_). Assistive-technology users still receive an announcement on the changed region.
+
 Events that raise toasts include:
 
-- Snippet actions: creating, duplicating, deleting, publishing a draft, and reverting/discarding a draft.
-- Dataset actions: creating, deleting, and extracting inline data into a dataset.
+- Snippet actions: **duplicating** (the copy is easily mistaken for an edit of the original), **deleting** (the snippet disappears), **publishing** a draft, and **reverting** a draft. _Creating_ a snippet opens it in the editor and needs no toast.
+- Dataset actions: **deleting**, and **extracting** inline data into a dataset (the dataset is created off-screen while the user is in the editor). _Creating_ a dataset in the Datasets modal is confirmed by the new dataset appearing selected.
 - Import/Export: results of an import (success/partial/failure) and confirmation of an export.
 - Errors: spec/data validation failures and local-storage capacity warnings.
 
+**Copy Reference** (Datasets) is the exception that proves the rule: a clipboard write is invisible, but the universal pattern confirms it _inline on the control_ ("Copied"), announced politely to assistive tech — a toast per copy would be noise.
+
 ## G. Offline & Installable
 
 Astrolabe is local-first and usable without a network connection.

docs/spec/02-snippet-library.md

@@ -57,9 +57,9 @@ When a snippet is active, a metadata panel (within the left pane) exposes its ed
 
 ## Snippet Operations
 
-The library provides the lifecycle operations for snippets. Each operation gives clear feedback via a toast notification (see _Application Shell & Navigation_).
+The library provides the lifecycle operations for snippets. An operation whose outcome the user can't already see confirms it with a toast; an operation whose result is immediately visible needs none (see _Application Shell & Navigation_ → Toasts).
 
-- **Create New**: starts a new snippet from a small sample Vega-Lite bar-chart template (a few inline category/value rows), assigns it an auto-generated default name (see _Naming & Tags_), saves it, and makes it the active snippet.
+- **Create New**: starts a new snippet from a small sample Vega-Lite bar-chart template (a few inline category/value rows), assigns it an auto-generated default name (see _Naming & Tags_), saves it, and makes it the active snippet. Opening in the editor _is_ the confirmation, so no toast is raised.
 - **Duplicate**: creates an independent copy of the active snippet with a name suffixed "(copy)". The copy carries over the specification, comment, tags, and dataset references, gets fresh created/modified timestamps and a new identity, and becomes the active snippet. A success toast confirms the duplication.
 - **Delete**: permanently removes the active snippet after the user confirms a warning that the action cannot be undone. After deletion no snippet is active. A toast confirms the deletion.
 - These operations never affect other snippets.

docs/spec/05-datasets.md

@@ -84,11 +84,12 @@ The detail pane for a selected dataset shows:
 
 ## Actions
 
-Each action raises a confirming toast (or an error toast on failure).
+A destructive or off-screen outcome raises a confirming toast; an action whose result is immediately visible is confirmed by that change. Any action may raise an error toast on failure (see _Application Shell & Navigation_ → Toasts).
 
 - **Copy Reference** — copies the by-name reference object to the clipboard, ready to paste into a spec:
   `{ "data": { "name": "MyDataset" } }`
-- **New / Create New** — opens the create form in the detail pane with fields: **name** (required, unique), **source** toggle (Inline / URL), the **data** (a paste area for inline, a URL field for URL source), and an optional **comment**. Save is disabled until a name and valid data/URL are present. On success the new dataset is selected.
+  The clipboard write is invisible, so it is confirmed _inline on the control_ ("Copied"), announced politely to assistive technology — not a toast.
+- **New / Create New** — opens the create form in the detail pane with fields: **name** (required, unique), **source** toggle (Inline / URL), the **data** (a paste area for inline, a URL field for URL source), and an optional **comment**. Save is disabled until a name and valid data/URL are present. On success the new dataset is shown selected in the detail pane — that visible result is the confirmation, so no toast is raised (a dataset created _off-screen_ via Extract does toast; see _Spec Editor_).
 - **Edit** — rename, edit the comment, and update the data (re-paste inline data or refresh the URL). Updating inline data re-profiles it; the modified timestamp advances.
 - **Delete** — asks for confirmation ("Delete \"Name\"? This cannot be undone."), then removes the dataset and clears the selection.