Snippet naming: content-derived on publish, frozen on explicit rename

docs/spec/03-editor-and-drafts.md

@@ -45,6 +45,7 @@ Every snippet carries two versions of its spec: a **published** (stable) version
 
 - A **Publish** action promotes the current draft to become the published version (the two are made identical).
 - Publish is also triggered by the keyboard shortcut Cmd/Ctrl+S.
+- If the snippet's name is **app-picked** (never explicitly renamed by the user — the timestamp default, a builder-generated name, or an earlier derived one), publish re-derives it from the now-published content: the spec's `title` verbatim when present (string, line array, or `{ text }` forms), else a mark + encodings description in the Chart Builder's naming dialect (e.g. "Bar chart of count by Ship Mode"), else the existing name stands. A name the user has set is never rewritten (see _Snippet Library → Naming & Tags_).
 - The snippet's dataset references track the draft continuously (recomputed on auto-save, extract, and revert), so publish needs no special reference handling — promoting the draft simply carries the already-current references onto the published version (see _Datasets_ for reference linking).
 - A success toast confirms the snippet was published.
 - Publish is unavailable when no snippet is active.