starkernel: restate VM fleet heat transfer on the virtual tick

Punch list §25 item 2.1 complete.
vm_physics_touch() no longer takes a wall-clock timestamp -- it reads
fleet_heartbeat_tick_count internally, which is execution-paced
(vm_runtime.c:143), not wall-clock. VMPhysics.last_active_ns ->
last_active_tick, VMFleetTouchSample.elapsed_us -> elapsed_ticks, and a
new explicit `touched` flag replaces the old `> 0` sentinel (tick 0 is
a legitimate value a first touch can land on, unlike wall-clock ns).

Verified: three-architecture boot (amd64 x2, aarch64, riscv64), all
reaching ok> with identical dict_hash=0x3d4e1daf289da94f matching the
item-0.10 baseline. No new compiler warnings in the touched files.

Honestly flagged, not fixed: with Tripod pruned to Hera alone (item
0.1), vm_physics_touch()'s fan-out has no other live VM to pull heat
from, so the fleet-heat-sum acceptance criterion is trivially satisfied
rather than genuinely stress-tested -- a real check needs Phase 4's
multi-VM fleet. fleet_transfer_slope_q48's seed (65536/3) was
calibrated for elapsed microseconds and has not been re-fit for elapsed
ticks; left as-is rather than guessed, deferred to item 5.1's DoE work.

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

include/starkernel/capsule_vm_physics.h

@@ -78,13 +78,18 @@ void vm_physics_retire(uint32_t vm_id);
  * Called from the three existing dispatch primitives (VM-EXEC, VM-CALL,
  * VM-STEP) at the point they've already confirmed the target VM is
  * live. Pulls heat from the rest of the fleet toward the touched VM
- * (amount = elapsed * fleet_transfer_slope_q48 >> 16) and appends
+ * (amount = elapsed_ticks * fleet_transfer_slope_q48 >> 16) and appends
  * vm_id to the fleet's rolling touch-history window.
  *
+ * Restated on the virtual tick (FABRIC.md item 2.1, 2026-08-04): no
+ * longer takes a wall-clock timestamp. Reads fleet_heartbeat_tick_count
+ * internally, which is execution-paced (advanced once per vm_tick()
+ * call, see vm_physics_heartbeat_tick), so the transfer this produces is
+ * a deterministic function of the execution stream, not of wall time.
+ *
  * @param vm_id   Registry VM ID being dispatched to
- * @param now_ns  Current monotonic time in nanoseconds (timer_now_ns())
  */
-void vm_physics_touch(uint32_t vm_id, uint64_t now_ns);
+void vm_physics_touch(uint32_t vm_id);
 
 /**
  * vm_physics_tick - Heartbeat-gated inference pass