Ports the engine off the second JS runtime onto Node 26.3 (node:ffi) so the
repo ships a single JavaScript runtime: child_process for the gateway, vitest
for tests, an esbuild + Solid build step. Mouse selection copies the rendered
text you highlight, and the clipboard path is crash-proofed (a broken copy
pipe no longer quits the UI). Renames the engine dir ui-tui-opentui-v2/ ->
ui-opentui/ and updates the launcher/installer/Docker references.
