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/Signal/libsignal.ts

@@ -495,6 +495,7 @@ export function makeLibSignalRepository(
 
 			const decoded1 = jidDecode(fromJid)
 			if (!decoded1) {
+				logger.warn({ fromJid }, 'bulkDeviceMigration: failed to decode fromJid, aborting migration')
 				return { migrated: 0, skipped: 0, total: 0 }
 			}