Inviting someone who's already in AcceleratorApp now tells you

What's new

• Explicit duplicate-invite warning — the system tells you the user already exists, so you can take the right next step.
• No more "did that go through?" — clear feedback replaces silent rejection.

Why it matters

Silent failures are the worst class of bug: nothing breaks, but trust quietly erodes. People resend invites three times, ping the user on Slack, then file a support ticket. A two-line alert closes that loop in one second.