WIP: restore lost C behaviors (schtick message, forced redraw, greeting)

Incomplete checkpoint, preserved after the implementing session hit a
capacity limit partway through mutation verification. NOT reviewed and NOT
gate-clean: make fmt has not been run, so fmt-check currently fails on
ARCHITECTURE.md and TODO.md.

Work still outstanding before this is fit for review:
  - run make fmt and fold the result in
  - finish mutation-proving each of the three behaviors
  - verify every message string byte-for-byte against the C sources
  - confirm TestSeedCompatItemTables passes with its golden untouched

Refs #13.

game/autosave_test.go

@@ -457,6 +457,10 @@ func newBlockingTerm() *blockingTerm {
 
 func (t *blockingTerm) Render(*Window) {}
 
+// Repaint has nothing to redraw: this terminal exists for its input
+// behaviour, and no autosave test types CTRL-R.
+func (t *blockingTerm) Repaint() {}
+
 func (t *blockingTerm) Fini() {}
 
 // Interrupt wakes a blocked ReadChar; called from the saving goroutine.