fix(BUG-12): campaign selection follows activeDisplay

Selection effect had `!selectedCampaignId` guard — once any campaign
selected, new activeDisplay.activeCampaignId writes ignored. Replay tool
writes activeDisplay to new campaign each run; UI stayed on old selection
=> displayed wrong campaign data.

Removed guard. Selection now syncs when activeCampaignId differs from
current selection. Manual deselect (null) does not force-select (RED test
locks this).

Also fixed test helper bug: createCampaignViaUI/createEncounterViaUI
returned FIRST setDoc match (idA for all creates). Now filters by name +
.pop() for latest. This masked the real bug for several debug cycles.

Tests: 2 new (SelectionFollowsActiveDisplay), both green. No regressions
in full FE suite (App, Combat, DisplayView, Encounter, HideHpToggle,
Logs, Participant, storage all pass). Combat.scenario = pre-existing
BUG-11 crash, not regression.

src/App.js

@@ -2151,11 +2151,10 @@ function AdminView({ userId }) {
     if (
       initialActiveInfo &&
       initialActiveInfo.activeCampaignId &&
-      campaignsWithDetails.length > 0 &&
-      !selectedCampaignId
+      campaignsWithDetails.length > 0
     ) {
       const campaignExists = campaignsWithDetails.some(c => c.id === initialActiveInfo.activeCampaignId);
-      if (campaignExists) {
+      if (campaignExists && selectedCampaignId !== initialActiveInfo.activeCampaignId) {
         setSelectedCampaignId(initialActiveInfo.activeCampaignId);
       }
     }