Revert "Build post chat and attachment workflows"

This reverts commit 0b920da187.

backend/internal/users/invitations.go

@@ -25,8 +25,6 @@ type Invitation struct {
 	CreatedBy     *string    `json:"created_by"`
 	CreatedAt     time.Time  `json:"created_at"`
 	InvitationURL string     `json:"invitation_url,omitempty"`
-	EmailSent     bool       `json:"email_sent"`
-	EmailError    string     `json:"email_error,omitempty"`
 }
 
 type CreateInvitationInput struct {