fix(v3): the DoE row's cache and bucket hits are measured, not written as 0 (#142)

Captain Bob, 2026-11-12: "correct deficiencies". heartbeat_capture_tick_snapshot
wrote cache_hits_delta and bucket_hits_delta as 0 ("TODO: wire ..."), though
physics_hotwords_cache.c counts both. Now each is read from the VM's hot-words
cache as a delta since the previous tick, the way word_executions_delta is
(and after the cache's stats are reset, the count since then); a VM with no
cache has 0. word_executions_delta was measured already: doe_log.c's "TODO: 0"
for it was stale, and its three column notes are corrected.

kernel/tests/test_heartbeat_export.c, 4 checks: a VM in memory with a cache
whose counters the test sets, captured tick by tick. Against the code as it
was: 3 failures (the hits 0 where the cache counted 5 and 3, then 7 and 7).
Now: 0. Built for amd64, aarch64, riscv64 and the hosted v3. Shared v3 code,
under the ruling. v3 is not part of acceptance; no DoE has run since 2026-09-16.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017RzZgrf7V7Zk2iczBXDRbm

kernel/tests/Makefile

@@ -19,7 +19,8 @@ CC     ?= cc
 CFLAGS := -std=c99 -Wall -Wextra -Werror -O2 -g -I$(HERE) -I$(ROOT)/kernel/include \
           -I$(ROOT)/kernel/include/starkernel -I$(ROOT)/v3/include
 
-TESTS := test_gpt test_usb_config test_sk_v4_stop test_sk_v4_slots test_sk_v4_mint test_sk_v4_identity
+TESTS := test_gpt test_usb_config test_sk_v4_stop test_sk_v4_slots test_sk_v4_mint test_sk_v4_identity test_heartbeat_export
+SRC_test_heartbeat_export := $(ROOT)/v3/src/heartbeat_export.c
 SRC_test_sk_v4_identity := $(ROOT)/kernel/src/v4/sk_v4_identity.c $(ROOT)/kernel/src/v4/sk_v4_slots.c $(ROOT)/kernel/src/gpt.c
 EXTRA_test_sk_v4_identity := -D__STARKERNEL__ -I$(ROOT)/v4/include -DSTICK_GROW_MIN_BYTES=8000000000ULL -DSTICK_ARTEMIS_CAP_GIB=256ULL
 SRC_test_sk_v4_mint := $(ROOT)/kernel/src/v4/sk_v4_mint.c $(ROOT)/kernel/src/gpt.c