Revert HEARTBEAT-TICKS@ to vm->heartbeat.tick_count; FABRIC-2.md Section R:

find and fix the real ACL-TTL measurement bug (zuse session never
authenticated, ACL enforcement never active)

Two mistakes corrected in sequence, both documented in full in
FABRIC-2.md Section R:

1. HEARTBEAT-TICKS@ was swapped to read heartbeat_ticks() -- a newer,
   kernel-only ISR hardware-timer counter (src/starkernel/heartbeat.c,
   the M5 TIME-TRUST engine) -- based on a misreading of which counter
   "the one clock" law refers to. Reverted to vm->heartbeat.tick_count,
   Loop #7 "Adaptive Heartrate", the actual year-plus-old counter the
   whole physics runtime is built on. Removed the now-irrelevant
   HEARTBEAT-PERIOD-NS@ accessor added to diagnose the wrong counter's
   adaptive re-arm period. Three-arch QEMU re-acceptance: POST 1012/0/0
   on amd64/aarch64/riscv64, HEARTBEAT-TICKS@ confirmed returning 77
   (matching the original pre-heartbeat_ticks() acceptance) on all three.

2. The real bug, found after the revert: every "ACL enabled" measurement
   in this investigation (Section P's 18-cell campaign, Section Q's
   pilot) loaded ACL.4th and ran EXEC-DOE from the bare `ok>` prompt
   without ever authenticating a zuse session. repl.c:303 keeps
   emergency_console=1 until zuse_session=1; vm_core.c:755 skips the
   entire ACL check block (TTL decrement and acl_recheck()) whenever
   emergency_console is set. ACL was configured but never armed.
   capsules/zuse.4th's pre-existing self-pin bug means the documented
   automatic zuse activation doesn't work either (still flagged, not
   fixed) -- worked around by invoking the directly-registered
   ZUSE-AUTHENTICATE word explicitly.

Validated pilot (amd64, seed 12345, 30 reps, same build, disabled vs.
genuinely zuse-authenticated-enabled): +117 ticks, +0.0448% overhead.
Disabled-arm determinism double-confirmed (261064 ticks, exact repeat
on a fresh boot) -- the 117-tick difference is real signal, not noise.
Reconciles with the original ACL-RWT campaign's own heartbeat-tick
result (+0.0054%-0.0088%, same order of magnitude). Section P's
wall-clock numbers and Section Q's "instrument blind" conclusion are
both marked invalidated/corrected in place, not deleted.

n=1 per arm, one architecture -- not yet a full campaign. Scoped as
next step, not undertaken in this pass.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/word_source/starforth_words.c

@@ -47,7 +47,6 @@
 #include "../../include/vm.h"
 #ifdef __STARKERNEL__
 #include "starkernel/vm/arena.h"
-#include "starkernel/timer.h"
 #endif
 #include "include/vocabulary_words.h"
 #include "../../include/version.h"
@@ -798,23 +797,14 @@ static void starforth_word_zuse_authenticate(VM *vm)
  * @brief Read-only accessor for the canonical heartbeat tick counter
  *
  * Stack effect: ( -- n )
- * On the kernel build, pushes heartbeat_ticks() -- the ISR-driven hardware
- * timer tick count (src/starkernel/heartbeat.c), the one real clock in this
- * project. NOT vm->heartbeat.tick_count, which is a FORTH colon-word-dispatch
- * counter gated at a fixed cadence -- frozen during idle time and blind to
- * any cost that doesn't change control flow (see FABRIC-2.md Section Q).
- * On the hosted build (no ISR timer), falls back to vm->heartbeat.tick_count
- * since that's the only tick source available there.
- * Read-only: no corresponding store word exists or should exist.
+ * Pushes vm->heartbeat.tick_count -- Loop #7 "Adaptive Heartrate", the one
+ * clock this project's timing measurements are supposed to read, not host
+ * wall-clock. Read-only: no corresponding store word exists or should exist.
  * @param vm Pointer to the VM instance
  */
 static void starforth_word_heartbeat_ticks(VM* vm)
 {
-#ifdef __STARKERNEL__
-    vm_push(vm, (cell_t)heartbeat_ticks());
-#else
     vm_push(vm, (cell_t)vm->heartbeat.tick_count);
-#endif
 }
 
 /**