Entry point only: dispatch between the stdio MCP proxy and the window.
Deliberately tiny (2026-09-20 split) - the window itself, App and its
patch points live in app.rs, ITS OWN rust_library target, so that
tools/hotpatch/patch.sh never has to relink this executable to pick up
an edit there or in packages/panels. See app.rs's doc comment and
../CLAUDE.md.