improve: add warning logs to null guards and fix transferDevice error handling

- Add warning/debug logs to all null guard patterns (if (!x) return/continue)
  so that when these guards fire, the reason is visible in logs instead of
  being silently swallowed
- Fix jid-utils.ts transferDevice: throw Error instead of returning empty
  string '' which could propagate as an invalid JID
- process-message.ts: warn on creds.me missing, reactionKey missing,
  creationMsgKey missing, eventCreatorPn missing
- chats.ts: warn on sendPresenceUpdate/handlePresenceUpdate missing values
- event-buffer.ts: debug on chat/contact/group update missing id
- socket.ts: debug on sessionStartTime not set
- communities.ts: debug on dirty node not found
- libsignal.ts: warn on bulk migration jidDecode failure

https://claude.ai/code/session_01XaA7GwNaB6azTHFYQ8WEpB

src/WABinary/jid-utils.ts

@@ -131,7 +131,7 @@ export const transferDevice = (fromJid: string, toJid: string) => {
 	const deviceId = fromDecoded?.device || 0
 	const toDecoded = jidDecode(toJid)
 	if (!toDecoded) {
-		return ''
+		throw new Error(`transferDevice: failed to decode toJid "${toJid}"`)
 	}
 
 	const { server, user } = toDecoded