Fix addParticipants: slot by initiative instead of append

addParticipants (bulk add all characters) appended to list end, ignoring
initiative. Pre-combat list showed random order until start encounter.
Now slots each participant by initiative desc, preserves existing order +
drag ties. Matches addParticipant single-add semantics.

Tests: 5 bulk-add slot cases (turn.bulkadd.test.js).

shared/turn.js

@@ -479,14 +479,20 @@ async function addParticipant(encounter, participant, ctx) {
 }
 
 async function addParticipants(encounter, newParticipants, ctx) {
-  const updatedParticipants = [...(encounter.participants || []), ...newParticipants];
+  // Slot each new participant into list by initiative (desc), preserve
+  // existing order + drag-established ties. Matches addParticipant semantics.
+  let base = [...(encounter.participants || [])];
+  for (const np of newParticipants) {
+    const idx = slotIndexForInit(base, np.initiative);
+    base.splice(idx, 0, np);
+  }
   const names = newParticipants.map(p => p.name).join(', ');
-  const patch = { participants: updatedParticipants };
+  const patch = { participants: base, ...syncTurnOrder(base) };
   const log = {
     type: 'add_participants',
     message: `Added ${newParticipants.length} participant${newParticipants.length === 1 ? '' : 's'}: ${names}`,
     delta: { count: newParticipants.length },
-    undo: { participants: newParticipants },
+    undo: { participants: newParticipants, newTurnOrderIds: patch.turnOrderIds },
   };
   return commit(encounter, patch, log, ctx);
 }