tetris: register the # key (which emits XK_slash on this device) as pause

The physical # key produces XK_slash, not XK_numbersign, so add XK_slash
to the pause binding. The on-screen label still reads '# PAUSE'.

src/games/tetris.cpp

@@ -432,7 +432,10 @@ static void handle_key(KeySym ks) {
     case XK_space: case XK_0:
       if (state == PLAYING) { hard_drop(); }
       break;
-    case XK_p: case XK_3: case XK_numbersign: case XK_asterisk:
+    // Pause: P, 3, *, and the # key. NOTE: on this device the # key emits
+    // XK_slash (not XK_numbersign), so register slash too while the on-screen
+    // label still shows '#'.
+    case XK_p: case XK_3: case XK_numbersign: case XK_asterisk: case XK_slash:
       if (state == PLAYING) {
         state = PAUSED;
       } else if (state == PAUSED) {