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>

tst/modulepath_test.sh

@@ -99,9 +99,13 @@ printf '@eval :cwd *K_input_dir* os.getcwd() @\n' > "$T/setb/pycwd.kt"
 check " 5. :cwd changes the Python working directory" \
       "$T/setb" "$T/setb/pycwd.kt"
 
+# The first @eval renders nothing, so the document begins with the space
+# the author wrote before the "/": ktext keeps it (it trims only newlines
+# from the result, as Machine::apply and the Python binding do -- a leading
+# space is the indent of a txt block that opens a document; TODO #60).
 printf '@eval :cwd *K_input_dir* :shell true @ / @eval :shell pwd @\n' > "$T/setb/restore.kt"
 check " 6. the cwd is restored after the eval" \
-      "/ $T/elsewhere" "$T/setb/restore.kt"
+      " / $T/elsewhere" "$T/setb/restore.kt"
 
 mkdir -p "$T/sp ace"
 printf 'spaced\n' > "$T/sp ace/f.txt"