The markdown and decision sidebar readers gain a shared action bar. A new
lib/builtin/shared/reader_chrome.dart provides ReaderHistory (browser-style
back/forward stack — push truncates forward), a ReaderHistoryMixin that also
holds a single pin slot, and a ReaderActionBar widget. Both readers push to
history only on external selection; back/forward and jump-to-pin reload
in-place without re-publishing a selection (no bus churn / no decision-tab
re-trigger). The edit pencil opens the current doc in the editor
(editor.open) — the markdown path, or the decision's file_path.
T-189, T-190, T-191.
Co-Authored-By: Claude <noreply@anthropic.com>
jpmschweitzerandClaude
6d0f5f244c