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.

src/App.js

@@ -1084,8 +1084,14 @@ function ParticipantManager({ encounter, encounterPath, campaignCharacters }) {
       return;
     }
     try {
-      const { patch } = reorderParticipants(encounter, draggedItemId, targetId);
+      const { patch, log } = reorderParticipants(encounter, draggedItemId, targetId);
       await storage.updateDoc(encounterPath, patch);
+      if (log) {
+        logAction(log.message, { encounterName: encounter.name }, {
+          encounterPath,
+          updates: log.undo,
+        });
+      }
     } catch (err) {
       // drag invalid (id not found) — ignore
     }