feat(saolei): 交互玩扫雷每一步自动出 PNG

- play_saolei.tcl: k 每执行一个按键动作就存 shots/NNN_<按键>.png，并覆盖
  shots/latest.png（在 VS Code 里开着 latest.png 即可每步自动刷新）；新增 view 命令
- fb2png.py: 新增 --quiet（只写 PNG 不打印，供脚本批量截图）
- tb_saolei*.v: 仅格式调整（case 分支拆行），无语义变化
实测：k cuuuuc -> shots/001_c.png ... 006_c.png，每张 640x480 正常

pipelined-cpu/tools/play_saolei.tcl

@@ -16,9 +16,15 @@
 #   k p        只切换插旗模式开关（不点击）
 #   k z        复位（等于重新上电，回到开始界面）
 #   k uucc     可以连写：上、上、点、点
-#   shot       不按键，只重画一遍当前画面
+#   shot       不按键，只重画一遍当前画面 + 存一张 PNG
+#   view       用系统看图器打开最新那张 PNG
 #   help       键位说明
 #
+# 截图：k 每执行**一个**按键动作就自动存一张 PNG 到 shots/NNN_<按键>.png
+#       （可以直接放进报告），同时覆盖 shots/latest.png。
+#       在 VS Code 里打开 shots/latest.png，每次操作后它都会自动刷新 —— 这就是
+#       "每一步都能看到 PNG" 的用法。
+#
 # 原理：k 把字符写进 cmd.txt；tb_saolei_play 每 100 us 仿真时间轮询一次并执行按键，
 #       同时每 1 ms 把显存 dump 到 now.txt；k 再调 fb2png.py --term 把画面画到终端。
 #       仿真速度大约是 1 ms 仿真时间 = 0.5 s 墙钟，所以每步等 1~2 秒，比真实慢很多，
@@ -67,12 +73,38 @@ proc help {} {
     puts "   k u/d/l/r   move cursor up/down/left/right (w/s/a/d work too)"
     puts "   k f         click in flag mode     k p   toggle flag switch only"
     puts "   k z         reset                  k uucc  several actions at once"
-    puts "   shot        redraw      help    this text      quit    exit"
-    puts "   PNG screenshot: py \"$::fb2png\" now.txt shot.png"
+    puts "   shot        redraw+screenshot       view   open latest PNG"
+    puts "   help        this text               quit   exit"
+    puts "   every key saved one PNG: shots/NNN_<key>.png   and  shots/latest.png"
     puts "  ---------------------------------------------------------------------------"
 }
 
-# one step: send the key -> advance simulation -> redraw
+# ---- every step saves one PNG: shots/001_c.png ... plus shots/latest.png ----
+set shot_dir "shots"
+file mkdir $shot_dir
+set shot_n 0
+
+proc save_shot {tag} {
+    global fb2png shot_dir
+    if {![file exists "now.txt"]} { return }
+    incr ::shot_n
+    set name [format "%s/%03d_%s.png" $shot_dir $::shot_n $tag]
+    if {[catch { exec py $fb2png --quiet now.txt $name } err]} {
+        puts "     (screenshot failed: $err)"
+        return
+    }
+    catch { file copy -force $name "$shot_dir/latest.png" }
+    puts "     png -> $name"
+}
+
+proc view {} {
+    global shot_dir
+    set f [file normalize "$shot_dir/latest.png"]
+    if {![file exists $f]} { puts "  (no screenshot yet)"; return }
+    catch { exec cmd /c start "" $f }
+}
+
+# one step: send the key -> advance simulation -> save PNG -> redraw
 proc k {keys} {
     set s [string map {" " "c"} [string tolower $keys]]
     foreach ch [split $s ""] {
@@ -80,11 +112,15 @@ proc k {keys} {
         puts "  >> $ch"
         send_char $ch
         run 1500 us
+        save_shot $ch
     }
     render
 }
 
-proc shot {} { render }
+proc shot {} {
+    save_shot "shot"
+    render
+}
 
 # ---- opening: run a little so the start screen is drawn, then show it ----
 help