Fix: give MatrixClient a real store so client.getRoom() works

The default StubStore.getRoom() always returns null, so every received
message bailed at the room lookup ('got m.room.message for unknown room').
A MemoryStore keeps joined rooms available for lookup.

index.js

@@ -1,5 +1,6 @@
 import * as dotenv from 'dotenv';
 import { MatrixClient } from 'matrix-js-sdk';
+import { MemoryStore } from 'matrix-js-sdk/lib/store/memory.js';
 import fs from 'fs';
 
 dotenv.config();
@@ -9,6 +10,7 @@ console.log('🚀 Starting Ancestor Quote Bot...\n');
 const client = new MatrixClient({
     accessToken: process.env.MATRIX_ACCESS_TOKEN,
     baseUrl: process.env.MATRIX_HOME_SERVER,
+    store: new MemoryStore(),
 });
 
 function loadQuotes() {