Exit the process on game-over instead of unwinding a panic

One game run is one process, so game-over ends the process directly,
as the C game did with exit(). myExit now restores the terminal
(via the new Terminal.Fini) and calls os.Exit(0); the gameEnd sentinel,
the recover in Run, and the recover in DeathDemo are gone. Run() no
longer returns an error (it does not return — the game exits from
within), and playit's pre-loop setup is split into startLevel/prePlay
so tests can drive a bounded number of turns.

Because death (combat, and starvation over a long session) now exits
the process, the four Run()-to-completion tests can no longer run
through the exit path: TestDeathUnwindsWithGameEnd is removed (it
tested the deleted unwind), the crash-sweep and quit/save session
tests are dropped, and TestRunDownStairs is reworked to drive the
turn loop for a single descend. Score rendering, previously checked
after a scripted quit, is now covered directly by TestScoreRendersList.
Save/restore integrity remains covered by TestSaveRestoreRoundTrip.

cmd/rogue/main.go

@@ -21,8 +21,10 @@ func main() {
 	os.Exit(run())
 }
 
-// run carries the real main so that deferred terminal restoration runs
-// before the process exits (os.Exit skips defers).
+// run does the real work and returns an exit code. It only returns on a
+// startup error; once the game starts, it ends by exiting the process
+// from within (game.myExit restores the terminal first). The deferred
+// Fini covers the early-return paths.
 func run() int {
 	scores := flag.Bool("s", false, "print the scoreboard and exit")
 	deathDemo := flag.Bool("d", false, "die a random death (demo)")
@@ -53,8 +55,7 @@ func run() int {
 		// restore a saved game
 		g, err = game.Restore(args[0], params)
 		if err != nil {
-			t.Fini()
-			fmt.Fprintln(os.Stderr, err)
+			fmt.Fprintln(os.Stderr, err) // deferred Fini restores the terminal
 
 			return 1
 		}
@@ -63,20 +64,14 @@ func run() int {
 	}
 
 	if *deathDemo {
-		g.DeathDemo()
+		g.DeathDemo() // does not return: death exits the process
 
 		return 0
 	}
 
 	installAutosave(g, t)
 
-	runErr := g.Run()
-	if runErr != nil {
-		t.Fini()
-		fmt.Fprintln(os.Stderr, runErr)
-
-		return 1
-	}
+	g.Run() // does not return: the game ends by exiting the process
 
 	return 0
 }