Width and height argtypes, kdesc --argtypes from ref/, txt @define/@left_right/@columns, kdiag --check value validation (from dev d6993110e9b3)

Also: the klammertext argtype (descriptions kept as source), txt table
wrapping and :hpos/:offset, @c between ‹ ›, txt section headings, the
ktext newline-only trim, capitalize(), and the argtype test suite.

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

sks/section/section.py

@@ -72,6 +72,5 @@ class Section(klammer_base.Klammer_base):
         result = f"%__sectionlink__{id}__{self.title}__" + "\n" + result
         return result
 
-# Need to implement the procedural numbering for the txt target
-#    def txt(self):
-#        return self.title
+    def txt(self):
+        return f"@b {self.title} @"