Populate campaign players array in combat replay and scenario

Both combat.js replay and Combat.scenario.test.js built character participants
inline via buildCharacterParticipant without persisting to campaign doc. Real
app stores chars in campaign doc players array; encounter participants built
from that. Replay/scenario diverged from real flow — campaign had zero chars.

Fix:
- replay.js: roster chars now have id, persisted to campaign doc players array
  at setup_campaign step
- Combat.scenario.test.js: addCharacterViaUI writes char to campaign doc
  players array (mirrors app), CAMPAIGN_PATH const added

scripts/combat/replay.js

@@ -41,9 +41,9 @@ const pick = (arr) => arr[Math.floor(Math.random() * arr.length)];
 
 function buildRoster() {
   return [
-    { name: 'Fighter', defaultMaxHp: 200, defaultInitMod: 2 },
-    { name: 'Cleric', defaultMaxHp: 180, defaultInitMod: 1 },
-    { name: 'Rogue', defaultMaxHp: 160, defaultInitMod: 3 },
+    { id: 'char-fighter', name: 'Fighter', defaultMaxHp: 200, defaultInitMod: 2 },
+    { id: 'char-cleric', name: 'Cleric', defaultMaxHp: 180, defaultInitMod: 1 },
+    { id: 'char-rogue', name: 'Rogue', defaultMaxHp: 160, defaultInitMod: 3 },
   ];
 }
 function buildMonsters() {
@@ -239,6 +239,7 @@ module.exports = async function replay(args) {
   await callStep('setup_campaign', { campaignId }, async () =>
     storage.setDoc(getPath.campaign(campaignId), {
       id: campaignId, name: `Replay Campaign ${runStamp}`, createdAt: Date.now(),
+      players: buildRoster(),
     })
   );
   await callStep('setup_encounter', { encounterId }, async () =>