feat: add inbound username support and USync username protocol

Aligns with Baileys upstream PR #2480. WhatsApp is rolling out an
inbound username field that maps to the user's LID. This change is
purely additive — it captures and propagates the new optional field
through types, decoders, USync queries, and group/contact events.

Skipped intentionally to preserve InfiniteAPI's LID/PN customization:
- handleGroupNotification in messages-recv.ts (custom LID->PN flow on
  groups.upsert / participants.map). Username for these specific
  events still flows via process-message's emitParticipantsUpdate
  (reads message.key.participantUsername added in decode-wa-message).

Carousel/buttons code (messages.ts, messages-send.ts) untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Utils/process-message.ts

@@ -763,12 +763,19 @@ const processMessage = async (
 				id: jid,
 				author: message.key.participant!,
 				authorPn: message.key.participantAlt!,
+				authorUsername: message.key.participantUsername!,
 				participants,
 				action
 			})
 		const emitGroupUpdate = (update: Partial<GroupMetadata>) => {
 			ev.emit('groups.update', [
-				{ id: jid, ...update, author: message.key.participant ?? undefined, authorPn: message.key.participantAlt }
+				{
+					id: jid,
+					...update,
+					author: message.key.participant ?? undefined,
+					authorPn: message.key.participantAlt,
+					authorUsername: message.key.participantUsername
+				}
 			])
 		}
 
@@ -777,6 +784,7 @@ const processMessage = async (
 				id: jid,
 				author: message.key.participant!,
 				authorPn: message.key.participantAlt!,
+				authorUsername: message.key.participantUsername!,
 				participant: participant.lid,
 				participantPn: participant.pn,
 				action,