match main firebase behavior; fix contract + mismatches

Contract rewritten to match main prod truth:
- require id injection in all doc/collection results
- honor setDoc({merge:true}) (main L1624 + 4 activeDisplay sites)
- drop invented bare<->prefixed cross-lookup tests (main never does this)
- add setDoc{merge}, batch set-only/update-only contract coverage

Fix mismatches vs main:
- subscribeCollection hook now forwards queryConstraints (was dropped;
  LOG_QUERY sort+limit honored again). Mock onSnapshot honors orderBy+limit.
  2 new contract tests prove the chain.
- subscribeDoc/subscribeCollection adapters now forward errCb. App hooks +
  DisplayView propagate subscribe errors to UI (match main onSnapshot 3rd arg).
- ws adapter signatures accept queryConstraints + errCb (interface match).

activeDisplay writes match main:
- 5 unguarded sites -> setDoc({merge:true}) (create-if-missing, not updateDoc)
- 3 guarded sites stay updateDoc

Delete memory adapter: third storage system added complexity, zero value.
firebase-mock covers fast tests, ws covers server path. Factory throws on
unknown mode now.

Delete phantom 'Phase A/B' comment in firebase.js header.

Tests updated to assert setDoc{merge} (not updateDoc) for activeDisplay writes.
83/83 green.

src/storage/index.js

@@ -12,7 +12,6 @@ import {
 } from 'firebase/firestore';
 import { initFirebase, createFirebaseStorage } from './firebase';
 import { createWsStorage } from './ws';
-import { createMemoryStorage } from './memory';
 
 let storageInstance = null;
 
@@ -30,7 +29,7 @@ export function getStorage() {
       wsUrl: process.env.REACT_APP_BACKEND_WS || '',
     });
   } else {
-    storageInstance = createMemoryStorage();
+    throw new Error(`Unknown REACT_APP_STORAGE mode: ${mode}. Use 'firebase' or 'ws'.`);
   }
   return storageInstance;
 }