fix(turn): log reorder + deathSave (BUG-7)

reorderParticipants returned log:null → handler skipped logAction → drag
invisible in combat log, no undo payload. Now returns
log:{ message, undo:{ participants, turnOrderIds, currentTurnParticipantId }}.
App.js handleDrop calls logAction on logged reorders.

Found second gap: deathSave also returned null log (both branches).
Fixed — message + undo (participants snapshot).

Added logging contract test (turn.logging.test.js):
- all mutating ops logged (start/next/pause/add/remove/toggle/hp/deathsave/
  condition/reorder/end)
- no-ops return null log (same-id, cross-init, cross-pointer blocks)
- undo payloads valid + restore prior state
- documents addParticipants + updateParticipant gaps (null log, intentional)

235 tests green.

TODO.md

@@ -4,9 +4,13 @@ Backlog of bugs + long-term items. Milestones live in REWORK_PLAN.md.
 
 ## Open bugs
 
-### BUG-7: reorderParticipants has no undo
-- `reorderParticipants` returns `log: null`. Other ops return `log.undo`.
-- Cannot undo drag-drop. Candidate for undo system (M6).
+### BUG-7: reorderParticipants not logged
+- FIXED — now returns `log: { message, undo }`. Handler calls logAction.
+  Undo snapshots participants[] + turnOrderIds + pointer.
+- Found second gap: deathSave also returned null log. Fixed (message + undo).
+- Logging contract test added: turn.logging.test.js (all mutating ops logged,
+  no-ops null, undo payloads valid). Documents addParticipants +
+  updateParticipant gaps (null log, intentional).
 
 ## Open features