fix: add generate-tool-belt-prompt alias for cognitive-tool-prompt

Another naming drift: think() calls generate-tool-belt-prompt but the
actual function was cognitive-tool-prompt in core-defpackage.

org/core-defpackage.org

@@ -270,6 +270,10 @@ Tools that the LLM can invoke are registered here. Each tool has a name, descrip
     (if descriptions
         (format nil "Available tools:~%~a" (apply #'concatenate 'string (sort descriptions #'string<)))
         "No tools registered.")))
+
+;; Alias: generate-tool-belt-prompt → cognitive-tool-prompt
+(defun generate-tool-belt-prompt ()
+  (cognitive-tool-prompt))
 #+end_src
 
 *** Centralized logging (log-message)