fix(turn): log addParticipants + updateParticipant (logging gaps)

addParticipants + updateParticipant returned log:null → invisible in
combat log. Contract test caught them. Now both return
log:{ message, undo:{ participants }}.

App.js handlers wired (handleAddAllCharacters, handleUpdateParticipant,
handleInlineInitiative) — call logAction on logged mutations.

Logging contract now complete: every mutating combat op produces a log
entry. No gaps. turn.logging.test.js proves it.

238 tests green.

shared/turn.js

@@ -333,8 +333,16 @@ function addParticipant(encounter, participant) {
 
 // ADD_PARTICIPANTS — bulk add (e.g. "add all campaign characters").
 function addParticipants(encounter, newParticipants) {
+  const undo = { participants: encounter.participants || [] };
   const updatedParticipants = [...(encounter.participants || []), ...newParticipants];
-  return { patch: { participants: updatedParticipants }, log: null };
+  const names = newParticipants.map(p => p.name).join(', ');
+  return {
+    patch: { participants: updatedParticipants },
+    log: {
+      message: `Added ${newParticipants.length} participant${newParticipants.length === 1 ? '' : 's'}: ${names}`,
+      undo,
+    },
+  };
 }
 
 // UPDATE_PARTICIPANT — edit modal save (name/initiative/hp/isNpc).
@@ -346,14 +354,28 @@ function updateParticipant(encounter, participantId, updatedData) {
   // SLOT only if initiative changed. Other edits (name/hp/notes/isNpc) = no
   // position change (design doc). Re-slots on unrelated edits shuffle the
   // list mid-round → rotation dupes.
+  const undo = { participants: encounter.participants || [] };
   if (!('initiative' in updatedData) || updatedData.initiative === target.initiative) {
     const sameSlot = existing.map(p => p.id === participantId ? merged : p);
-    return { patch: { participants: sameSlot, ...syncTurnOrder(sameSlot) }, log: null };
+    const fields = Object.keys(updatedData).join(', ');
+    return {
+      patch: { participants: sameSlot, ...syncTurnOrder(sameSlot) },
+      log: {
+        message: `${target.name} updated (${fields})`,
+        undo,
+      },
+    };
   }
   const without = existing.filter(p => p.id !== participantId);
   const idx = slotIndexForInit(without, merged.initiative);
   without.splice(idx, 0, merged);
-  return { patch: { participants: without, ...syncTurnOrder(without) }, log: null };
+  return {
+    patch: { participants: without, ...syncTurnOrder(without) },
+    log: {
+      message: `${target.name} updated (initiative: ${merged.initiative})`,
+      undo,
+    },
+  };
 }
 
 // REMOVE_PARTICIPANT — verbatim from ParticipantManager.confirmDeleteParticipant