fix: harden session error handling, normalizer null guard, extract redis-connection

- Wrap groupFetchAllParticipating in try/catch to prevent unhandled rejection on connect
- Catch errors from async onMessage/onGroups callbacks via Promise.resolve().catch
- Return null from normalizer when key.id is missing (prevents empty upsert key collision)
- Extract parseRedisUrl to redis-connection.ts to eliminate duplication

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/worker/src/whatsapp/normalizer.ts

@@ -35,10 +35,13 @@ export function normalizeMessage(msg: proto.IWebMessageInfo): NormalizedMessage
 
   if (!msg.message) return null;
 
+  const platformMsgId = key.id;
+  if (!platformMsgId) return null;
+
   const content = extractText(msg);
 
   return {
-    platformMsgId: key.id ?? '',
+    platformMsgId,
     sourceGroupJid: remoteJid,
     senderJid: key.participant ?? '',
     senderName: msg.pushName ?? undefined,