fix(channels): include display name in [From:] annotation for Telegram and WhatsApp

Telegram: senderLabel now includes full name alongside username, e.g.
[From: @nguyennlt (Nguyễn Trần)] instead of just [From: @nguyennlt].
Also uses FirstName + LastName when no username is set.

WhatsApp: add missing [From:] annotation — was the only channel not
annotating sender identity for the LLM.

internal/channels/telegram/handlers.go

@@ -226,9 +226,14 @@ func (c *Channel) handleMessage(ctx context.Context, update telego.Update) {
 	}
 
 	// Compute sender label for group context (used in history + current message annotation)
-	senderLabel := user.FirstName
+	displayName := strings.TrimSpace(user.FirstName + " " + user.LastName)
+	senderLabel := displayName
 	if user.Username != "" {
-		senderLabel = "@" + user.Username
+		if displayName != "" {
+			senderLabel = "@" + user.Username + " (" + displayName + ")"
+		} else {
+			senderLabel = "@" + user.Username
+		}
 	}
 
 	// --- Group mention gating (matching TS mentionGate logic) ---

internal/channels/whatsapp/whatsapp.go

@@ -274,6 +274,11 @@ func (c *Channel) handleIncomingMessage(msg map[string]any) {
 		cc.EnsureContact(ctx, c.Type(), c.Name(), senderID, senderID, metadata["user_name"], "", peerKind, "user")
 	}
 
+	// Annotate with sender identity so the agent knows who is messaging.
+	if senderName := metadata["user_name"]; senderName != "" {
+		content = fmt.Sprintf("[From: %s]\n%s", senderName, content)
+	}
+
 	c.HandleMessage(senderID, chatID, content, media, metadata, peerKind)
 }