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-perceive.lisp

@@ -16,9 +16,7 @@
 FN receives (signal) and returns T if consumed, nil to continue."
   (setf (gethash sensor *pre-reason-handlers*) fn))
 
-;; Alias for backward compatibility
 (defun inject-stimulus (raw-message &key stream (depth 0))
-  "Alias for stimulus-inject."
   (stimulus-inject raw-message :stream stream :depth depth))
 
 (defun stimulus-inject (raw-message &key stream (depth 0))
@@ -53,10 +51,6 @@ FN receives (signal) and returns T if consumed, nil to continue."
           (skip-event ()
             (log-message "SYSTEM RECOVERY: Stimulus dropped."))))))
 
-;; Alias: perceive-gate → loop-gate-perceive
-(defun perceive-gate (signal)
-  (loop-gate-perceive signal))
-
 (defun loop-gate-perceive (signal)
   "Stage 1 of the metabolic pipeline: Normalize sensory input."
   (let* ((payload (getf signal :payload))
@@ -110,6 +104,9 @@ FN receives (signal) and returns T if consumed, nil to continue."
     (setf (getf signal :foveal-focus) *loop-focus-id*)
     signal))
 
+(defun perceive-gate (signal)
+  (loop-gate-perceive signal))
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
   (ql:quickload :fiveam :silent t))