refactor: split the TUI and refresh project docs

Move login state, authentication, discovery, input, rendering, and tests into focused TUI modules. Add detailed CLI error reports with recovery commands, align the build and host-check documentation, and keep the legacy Go tree outside normal builds.

Checks: make check; make integration-test; go test ./... (legacy/go).

legacy/go/tui/bg/automata.go

@@ -1,5 +1,5 @@
-// The renderer packs two cell rows into each Unicode half-block row.
-// Two buffers let Tick update the grid without an allocation per frame.
+// Pack two cell rows into each Unicode half-block row; two buffers keep frame
+// updates allocation-free.
 package bg
 
 import (