Images in plain text and the terminal; bounded build parallelism (from dev 16f82cc887af)

- @image under txt and ansi is a picture in characters, in five styles
  (Image_txt_style: halfblock the default, shade, ascii, quadrant,
  braille), sized to the terminal's width less a margin when ktext runs
  in one, every cell in its own colours under ansi; a figure's caption
  is centred under it and no txt caption is ruled off any more.
- The build compiles as many files at once as the machine has cores
  (JOBS; make -C com JOBS=1 for a small machine): the sub-makes' bare -j
  meant unlimited parallelism and exhausted 8 GB machines. The three
  install pages say "make -C com".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

sks/code/code_block.py

@@ -379,12 +379,10 @@ class Code(klammer_base.Klammer_base):
         width = max(len(line.rstrip()) for line in lines)
         rule = indent + klammer_base.hide_typographic("-" * width)
         body = [indent + prepared(line) for line in lines]
-        # A caption above the listing is ruled off by the caption pass, so
-        # the listing draws its own top rule only when nothing does.
-        captioned = self.number or self.caption
-        caption_above = captioned and self.caption_side in ("top", "left")
-        if not caption_above:
-            body.insert(0, rule)
+        # The listing's frame is its own: a rule above and below, whether
+        # or not a caption stands over it (the caption pass draws no rule,
+        # 2026-09-28 -- no target rules a caption off).
+        body.insert(0, rule)
         body.append(rule)
         result = phases.txt_lay_out("\n".join(body))
         return txt_util.add_caption(