Document language for dates; @eval pathname resolution and :cwd (from dev bc7cd62b6f68)

@date/@datetime gain :lang (German: "16. Juni 1910") over a document-wide
Language state variable, and :number for the numeric form (en 6/16/1910,
de 16.06.1910 per DIN 5008).  @eval finds Python modules next to the file
that names them regardless of the cwd, and the new :cwd option runs an
eval in a chosen working directory (@source_file uses it to resolve
against the document).  Two new test suites ship in tst/.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tst/Makefile

@@ -1,10 +1,11 @@
 # Klammertext distribution test suite (subset).
 #
-# Runs the five shell regression suites:
+# Runs the six shell regression suites:
 #   cond_test.sh     — @cond argument delimitation
 #   deftype_test.sh  — the four klammer definition modes + redefinition table
 #   escape_test.sh   — target character escaping and quoted specials
 #   filename_test.sh — filenames with spaces (quoting, " / " lists, rescue)
+#   modulepath_test.sh — @eval finds modules beside the file that names them
 #   editor_test.sh   — editor support (doc/edit): indentation and table
 #                      alignment; needs python3, uses Emacs when installed
 #
@@ -16,4 +17,5 @@ test:
 	./deftype_test.sh
 	./escape_test.sh
 	./filename_test.sh
+	./modulepath_test.sh
 	./editor_test.sh