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/__mocks__/firebase/firestore.js

@@ -19,7 +19,11 @@ export function limit(n) { return { __type: 'limit', n }; }
 // writes
 export async function setDoc(docRef, data, opts) {
   recordCall({ fn: 'setDoc', path: docRef.path, data: clone(data), opts: opts || null });
-  MOCK_DB.set(docRef.path, clone(data));
+  if (opts && opts.merge) {
+    MOCK_DB.merge(docRef.path, clone(data));
+  } else {
+    MOCK_DB.set(docRef.path, clone(data));
+  }
   return undefined;
 }
 export async function updateDoc(docRef, patch) {
@@ -70,6 +74,7 @@ export async function getDocs(collRefOrQuery) {
 // realtime — emit from mock DB, capture unsub
 export function onSnapshot(refOrQuery, onSuccess, onError) {
   const path = refOrQuery.path || (refOrQuery.ref && refOrQuery.ref.path);
+  const constraints = refOrQuery.constraints || [];
   // fire immediately with current state
   const emit = () => {
     if (refOrQuery.__ref && refOrQuery.path && path.split('/').length % 2 === 0) {
@@ -80,7 +85,8 @@ export function onSnapshot(refOrQuery, onSuccess, onError) {
         data: () => data,
       });
     } else {
-      const docs = MOCK_DB.collection(path);
+      let docs = MOCK_DB.collection(path);
+      docs = applyConstraints(docs, constraints);
       onSuccess({ docs: docs.map(d => ({ id: d.id, data: () => d.data })) });
     }
   };
@@ -90,6 +96,27 @@ export function onSnapshot(refOrQuery, onSuccess, onError) {
   return unsub;
 }
 
+// Apply Firestore-style query constraints (orderBy desc/asc, limit) to mock docs.
+// Mirrors real SDK semantics enough for contract tests. Only orderBy + limit
+// supported (App's LOG_QUERY uses exactly these).
+function applyConstraints(docs, constraints) {
+  let out = [...docs];
+  for (const c of constraints) {
+    if (c.__type === 'orderBy') {
+      out.sort((a, b) => {
+        const av = a.data[c.field];
+        const bv = b.data[c.field];
+        if (av === bv) return 0;
+        const cmp = av > bv ? 1 : -1;
+        return c.dir === 'desc' ? -cmp : cmp;
+      });
+    } else if (c.__type === 'limit') {
+      out = out.slice(0, c.n);
+    }
+  }
+  return out;
+}
+
 function clone(v) {
   if (v === null || v === undefined) return v;
   return JSON.parse(JSON.stringify(v));