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/src/doe_log.c

@@ -36,9 +36,9 @@
  *   1.  tick_number           uint32  — monotonic heartbeat counter
  *   2.  elapsed_ns            uint64  — ns since run start
  *   3.  tick_interval_ns      uint64  — actual interval from prior tick
- *   4.  cache_hits_delta       uint32  — hot-words cache hits this tick (TODO: 0)
- *   5.  bucket_hits_delta      uint32  — bucket hits this tick (TODO: 0)
- *   6.  word_executions_delta  uint32  — words executed this tick (TODO: 0)
+ *   4.  cache_hits_delta       uint32  — hot-words cache hits this tick (measured since #142)
+ *   5.  bucket_hits_delta      uint32  — bucket hits this tick (measured since #142)
+ *   6.  word_executions_delta  uint32  — words executed this tick (measured; the "TODO: 0" here was stale)
  *   7.  hot_word_count         uint64  — words with heat >= threshold
  *   8.  avg_word_heat_q48      uint64  — mean execution heat as raw Q48.16 integer
  *   9.  window_width           uint32  — rolling window effective size