test(raft-ha-core-safety): chaotic soak mode + isolated verdict (task 1.2)

Opt-in overlapping-kill mode (kills inside election windows). Verdict
counts committed walcompare divergence + committed-job loss; bug-854
(client discovery) and bug-924 (overlayfs fdatasync) counted separately
and excluded from PASS/FAIL. 17/17 verdict self-test GREEN. Live smoke
corroborated chaotic regime + live bug-854 isolation.

.kiro/specs/raft-ha-core-safety/tasks.md

@@ -13,7 +13,7 @@
   - _Requirements: 7.1, 7.5_
   - _Boundary: Deterministic Chaotic Harness_
 
-- [ ] 1.2 Add a chaotic soak mode with an isolated verdict
+- [x] 1.2 Add a chaotic soak mode with an isolated verdict
   - Add an overlapping-kill mode to the soak driver (kills landing inside election windows, not only sequential kill→wait→rejoin); produce a verdict that counts `walcompare` divergences and committed-job loss while excluding client-discovery (bug-854) and overlayfs `fdatasync` (bug-924) failures from the divergence/job-loss result
   - Observable completion: the soak runs chaotic mode against real-fs release binaries and emits a verdict whose divergence/job-loss counts are unaffected by bug-854/bug-924
   - _Requirements: 7.5, 8.4_