docs(specs): gap-analysis validation pass across all 9 HA-family specs

Appended "Gap Analysis — Validation Pass (2026-06-09)" to each spec's
research.md with requirement-to-asset maps, status tags, and effort/risk.

Key outcomes:
- ha-repl-hardening: REOPENED with task series 7.1-7.7 — replication
  payload data plane is missing (snapshot chunks and WAL catch-up ship
  header-only; standbys converge on LSN without holding entity state)
- worker-join-refactor, resval-id-decoupling: marked implemented
  (all criteria re-verified, full test suite green)
- buglog: 335/336 (scheduler dequeue, open), 337/338/339 (fixed in
  previous commit); cerebrum Decision Log corrected (term-only vote
  deny was recorded as intentional but was a regression)

.kiro/specs/worker-join-refactor/spec.json

@@ -1,9 +1,9 @@
 {
   "feature_name": "worker-join-refactor",
   "created_at": "2026-05-15T00:00:00Z",
-  "updated_at": "2026-05-15T03:20:00Z",
+  "updated_at": "2026-06-09T17:45:00Z",
   "language": "en",
-  "phase": "tasks-generated",
+  "phase": "implemented",
   "approvals": {
     "requirements": {
       "generated": true,