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

src/tests/Combat.scenario.test.js

@@ -56,7 +56,7 @@ let display = {
   hideNpcHp: false,
 };
 const CAMPAIGN_ID = 'camp-1';
-const roster = [];
+const CAMPAIGN_PATH = `campaigns/${CAMPAIGN_ID}`;const roster = [];
 
 let storage, ctx;
 const DISPLAY_PATH = 'activeDisplay/status';
@@ -74,7 +74,16 @@ const any = (name) => enc.participants.find(p => p.name === name);
 const anyById = (id) => enc.participants.find(p => p.id === id);
 
 function addCharacterViaUI(name, maxHp, initMod) {
-  roster.push({ id: `char-${name}`, name, defaultMaxHp: maxHp, defaultInitMod: initMod });
+  const character = { id: `char-${name}`, name, defaultMaxHp: maxHp, defaultInitMod: initMod };
+  roster.push(character);
+  // persist to campaign doc (mirrors app: players array)
+  if (storage) {
+    const existing = (storage.docs.get(CAMPAIGN_PATH) || {}).players || [];
+    storage.setDoc(CAMPAIGN_PATH, {
+      id: CAMPAIGN_ID, name: 'Scenario Campaign', createdAt: Date.now(),
+      players: [...existing, character],
+    });
+  }
 }
 
 async function addMonsterParticipant(name, maxHp, initMod, asNpc = false) {