feat: more native menus with expected reactions

PLAN.md

@@ -4,23 +4,7 @@ Only unfinished implementation work belongs here. DwarfStar remains the
 behavioral oracle for model execution, token processing, context accounting,
 KV-cache behavior, the HTTP API, and the built-in agent loop.
 
-## 1. Finish native project and chat controls
-
-- Add functional File, View, and Help menus; update native menu enabled state
-  from the focused control; complete undo/redo behavior; and make transcript
-  text selectable and copyable.
-- File menu has an "export" menu to save a chat as markdown
-- File menu has a new "menu" that opens a new chat in the currently active
-  project. if the app is not on a project or session of a project in the
-  sidebar, "new" is disabled
-- View menu gets the "manage models" menu item, remove it from Window menu
-- View menu gets toggle menu for sidebar with hotkey cmd-B
-- Explain model/checkpoint mismatches where a session must rebuild context
-  instead of resuming its existing checkpoint.
-- the hellp menu must open a window with an actual documentation in it,
-  that still needs to be constructed from the information and implementation
-
-## 2. Add Dev Brain support
+## 1. Add Dev Brain support
 
 - Let the user select one Obsidian vault and give the local agent bounded
   Markdown memory_search, memory_read, memory_create, and memory_append