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/term_test.go

@@ -8,10 +8,18 @@ type testTerm struct {
 	input []byte
 	pos   int
 	tick  int
+	// repaints counts forced full redraws. Rendering is a no-op here, so
+	// counting is the only way a headless test can tell that CTRL-R asked
+	// for a repaint rather than an ordinary refresh — the two are
+	// indistinguishable in the window contents, which is the whole reason
+	// the bug this replaces went unnoticed.
+	repaints int
 }
 
 func (t *testTerm) Render(*Window) {}
 
+func (t *testTerm) Repaint() { t.repaints++ }
+
 func (t *testTerm) Fini() {}
 
 // Interrupt has nothing to wake: this terminal's ReadChar never blocks.