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-reason.org

@@ -279,12 +279,10 @@ The loop has retry logic: up to 3 attempts. If the deterministic engine rejects
 
 The retry limit prevents infinite loops. If the LLM cannot produce a passable proposal within 3 attempts, the last rejection reason is attached to the signal and the acted pipeline sees a failed reasoning cycle.
 
+*** loop-gate-reason
+
 ;; REPL-VERIFIED: 2026-05-03T13:00:00
 #+begin_src lisp
-;; Alias: reason-gate → loop-gate-reason
-(defun reason-gate (signal)
-  (loop-gate-reason signal))
-
 (defun loop-gate-reason (signal)
   (let* ((type (proto-get signal :type))
          (payload (proto-get signal :payload))
@@ -323,6 +321,18 @@ The retry limit prevents infinite loops. If the LLM cannot produce a passable pr
                 (return signal))))))))
 #+end_src
 
+*** reason-gate (backward-compatibility alias)
+
+The pipeline gate was originally named ~reason-gate~. Code that still
+uses the old name can call this alias. New code should call
+~loop-gate-reason~.
+
+;; REPL-VERIFIED: 2026-05-03T13:00:00
+#+begin_src lisp
+(defun reason-gate (signal)
+  (loop-gate-reason signal))
+#+end_src
+
 * Test Suite
 Verifies that the deterministic engine correctly rejects unsafe actions (like ~rm -rf /~) while allowing safe ones.
 #+begin_src lisp :tangle ../lisp/core-loop-reason.lisp