docs: add literate prose to naming-drift aliases and HITL gateway changes

Adds prose sections before every code block to satisfy the
prose-before-code discipline. Each backward-compatibility alias
(process-signal, perceive-gate, reason-gate, act-gate, inject-stimulus)
now has its own subsection explaining why it exists and what new code
should use instead.

Also:
- Fixes double #+end_src in core-loop-perceive.org
- Renames inject-stimulus → stimulus-inject in heartbeat-start and
  client-handle-connection (both already had aliases)
- Adds HITL interception prose to gateway-manager.org telegram/signal
  sections
- Splits Pre-Reason Handler Registry into two code blocks (defvar + defun)
  for one-per-block compliance

lisp/core-loop-act.lisp

@@ -96,10 +96,6 @@
           (t (format nil "TOOL [~a] RESULT: ~s" tool-name result))))
       (format nil "TOOL [~a] RESULT: ~a" tool-name result)))
 
-;; Alias: act-gate → loop-gate-act
-(defun act-gate (signal)
-  (loop-gate-act signal))
-
 (defun loop-gate-act (signal)
   "Final stage of the metabolic pipeline: Actuation.
 For approval-required actions, creates a Flight Plan instead of executing."
@@ -155,6 +151,9 @@ For approval-required actions, creates a Flight Plan instead of executing."
     (setf (getf signal :status) :acted)
     feedback))
 
+(defun act-gate (signal)
+  (loop-gate-act signal))
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
   (ql:quickload :fiveam :silent t))