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-act.org

@@ -193,12 +193,12 @@ The gate runs a last-mile deterministic check on the approved action before exec
 
 After dispatch, the gate captures any feedback produced by the actuation (tool output, error events) and returns it to the loop for the next cognitive cycle.
 
+*** loop-gate-act
+
+The main act pipeline stage.
+
 ;; REPL-VERIFIED: 2026-05-03T13:00:00
 #+begin_src lisp
-;; 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."
@@ -255,6 +255,18 @@ For approval-required actions, creates a Flight Plan instead of executing."
     feedback))
 #+end_src
 
+*** act-gate (backward-compatibility alias)
+
+The pipeline gate was originally named ~act-gate~. Code that still
+uses the old name can call this alias. New code should call
+~loop-gate-act~.
+
+;; REPL-VERIFIED: 2026-05-03T13:00:00
+#+begin_src lisp
+(defun act-gate (signal)
+  (loop-gate-act signal))
+#+end_src
+
 * Test Suite
 Verifies that the act gate correctly processes an approved action and sets the signal status to ~:acted~.
 #+begin_src lisp :tangle ../lisp/core-loop-act.lisp