Add v2 username lookup for meeting RSVP data

- Add Username field to inviteResponseInput struct for v2 system
- Implement username lookup using UserID (v1 platform ID) via lookupV1User
- Map username to Auth0 "sub" format using mapUsernameToAuthSub helper
- Add debug logging for successful lookups and warning for failures
- Follows same pattern as invitee and attendee username resolution

This allows the v2 system to associate RSVP responses with the correct user accounts.

Generated with [Claude Code](https://claude.com/claude-code)

Signed-off-by: Andres Tobon <andrest2455@gmail.com>

Author: andrest50

cmd/lfx-v1-sync-helper/handlers_meetings.go

@@ -686,6 +686,18 @@ func handleZoomMeetingInviteResponseUpdate(ctx context.Context, key string, v1Da
 		return
 	}
 
+	// If username is blank but we have a v1 Platform ID (user_id), lookup the username.
+	if inviteResponse.Username == "" && inviteResponse.UserID != "" {
+		if v1User, lookupErr := lookupV1User(ctx, inviteResponse.UserID); lookupErr == nil && v1User != nil && v1User.Username != "" {
+			inviteResponse.Username = mapUsernameToAuthSub(v1User.Username)
+			logger.With("user_id", inviteResponse.UserID, "username", v1User.Username).DebugContext(ctx, "looked up username for invite response")
+		} else {
+			if lookupErr != nil {
+				logger.With(errKey, lookupErr, "user_id", inviteResponse.UserID).WarnContext(ctx, "failed to lookup v1 user for invite response")
+			}
+		}
+	}
+
 	// Extract the invite response ID
 	inviteResponseID := inviteResponse.ID
 	if inviteResponseID == "" {

cmd/lfx-v1-sync-helper/models_meetings.go

@@ -506,6 +506,10 @@ type inviteResponseInput struct {
 	// UserID is the ID of the user that the invite response is associated with.
 	UserID string `json:"user_id" dynamodbav:"user_id"`
 
+	// Username is the LF username of the registrant that the invite response is associated with.
+	// This is a v2 only attribute, meaning the username is for an LF user in the v2 system.
+	Username string `json:"username"`
+
 	// Org is the organization of the registrant that the invite response is associated with.
 	Org string `json:"org" dynamodbav:"org"`