refactor(turn): remove dead computeTurnOrderAfterAddition

Zero call sites. Old turn-array addition logic, superseded by 1-list
slotIndexForInit model. Removed func, export, stale comment, and 3
characterization tests that only locked the dead func's behavior.

shared/turn.js

@@ -114,26 +114,6 @@ const computeTurnOrderAfterRemoval = (encounter, removedId, updatedParticipants)
 // current pointer — no re-sort anywhere except startEncounter.
 // Tie rule: insert AFTER existing same-init (preserves creation order).
 // NOTE: 1-list model — caller syncs participants[] in same pos as insert target.
-const computeTurnOrderAfterAddition = (encounter, addedId) => {
-  if (!encounter.isStarted) return {};
-  const currentIds = encounter.turnOrderIds || [];
-  if (currentIds.includes(addedId)) return {};
-  const added = (encounter.participants || []).find(p => p.id === addedId);
-  if (!added) return {};
-  // find first id with strictly lower initiative; insert before it (== after all >= )
-  const initOf = id => {
-    const p = (encounter.participants || []).find(x => x.id === id);
-    return p ? (p.initiative || 0) : 0;
-  };
-  const addedInit = added.initiative || 0;
-  let insertAt = currentIds.length;
-  for (let i = 0; i < currentIds.length; i++) {
-    if (initOf(currentIds[i]) < addedInit) { insertAt = i; break; }
-  }
-  return { insertAt }; // caller splices participants[] at this pos, then syncs
-};
-
-// ----------------------------------------------------------------------------
 // Participant factory (mirrors ParticipantManager.handleAddParticipant shape)
 // ----------------------------------------------------------------------------
 
@@ -326,7 +306,7 @@ function togglePause(encounter) {
 
 // ADD_PARTICIPANT — appends participant. (Initiative rolled by caller via build*.)
 // If encounter already started, also slot participant into turnOrderIds by
-// initiative (via computeTurnOrderAfterAddition).
+// initiative (slotIndexForInit). 1-list model.
 function addParticipant(encounter, participant) {
   if ((encounter.participants || []).some(p => p.id === participant.id)) {
     throw new Error(`Participant with id "${participant.id}" already exists in encounter.`);
@@ -630,7 +610,6 @@ module.exports = {
   sortParticipantsByInitiative,
   syncTurnOrder,
   computeTurnOrderAfterRemoval,
-  computeTurnOrderAfterAddition,
   makeParticipant,
   buildCharacterParticipant,
   buildMonsterParticipant,