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

org/core-loop.org

@@ -78,12 +78,12 @@ The function handles four failure modes:
   - High-depth errors (depth > 2) → dropped (avoids cascading failures)
 - **Unhandled error**: the handler-case catches everything, preventing any single bad signal from crashing the agent
 
+*** loop-process
+
+The main pipeline entry point.
+
 ;; REPL-VERIFIED: 2026-05-03T13:00:00
 #+begin_src lisp
-;; Alias: process-signal → loop-process (backward compatibility)
-(defun process-signal (signal)
-  (loop-process signal))
-
 (defun loop-process (signal)
   "The entry point to the Metabolic Pipeline: Perceive -> Reason -> Act."
   (let ((current-signal signal))
@@ -121,6 +121,18 @@ The function handles four failure modes:
                               :payload (list :sensor :loop-error :message (format nil "~a" c) :depth depth)))))))))))
 #+end_src
 
+*** process-signal (backward-compatibility alias)
+
+The pipeline entry point was originally named ~process-signal~. Code
+that still uses the old name can call this alias. New code should call
+~loop-process~.
+
+;; REPL-VERIFIED: 2026-05-03T13:00:00
+#+begin_src lisp
+(defun process-signal (signal)
+  (loop-process signal))
+#+end_src
+
 ** Heartbeat Mechanism
 
 The heartbeat is a background thread that fires every N seconds (configurable via ~HEARTBEAT_INTERVAL~ env var, default 60). On each tick, it:
@@ -159,8 +171,8 @@ The heartbeat signal is how background skills (Gardener, Scribe) get triggered w
                (when (>= *heartbeat-save-counter* (/ *memory-auto-save-interval* interval))
                  (setf *heartbeat-save-counter* 0)
                  (save-memory-to-disk))
-               (inject-stimulus
-                 (list :type :EVENT :payload (list :sensor :heartbeat :unix-time (get-universal-time))))))
+               (stimulus-inject
+                  (list :type :EVENT :payload (list :sensor :heartbeat :unix-time (get-universal-time))))))
            :name "passepartout-heartbeat"))))
 #+end_src
 #+end_src