Improve file dialogs and fix unsaved Kosmo tab closing

[elcritch]

Summary

• Improve the shared file browser used by Open and Save dialogs with a Places sidebar, editable location, status, and a file table that expands with the window.
• Fix Discard when closing an edited Kosmo tab, including while Moe remains in Insert mode. Remove the tab, select the next tab, and restore editor focus when the last file is closed.
• Attach unsaved changes confirmation to its owning window and preserve the order of other macOS document windows.
• Update the reliability documentation for released FigDraw 0.43.0.

Verification

• Rebased onto main after Improve Tekton performance and interface authoring #119; the base now requires FigDraw 0.43.0.
• atlas-run tests passed all four shared runners on macOS arm64 with Nim 2.2.12.
• atlas-run tests --compile-only examples/all_compile.nim compiled the example bundle.
• The shared test import check and formatting passed.
• Regression coverage includes file browser resizing and navigation, Discard in Moe Insert mode, replacement editor typing, and native window order.