listen exits 0 when the renderer fails to start #339

Problem

pkg/listen/proxy/renderer_interactive.go:56-63 only logs a Bubble Tea failure before closing doneCh:

go func() {
    if _, err := r.teaProgram.Run(); err != nil {
        log.WithField("prefix", "proxy.InteractiveRenderer").
            Errorf("Bubble Tea error: %v", err)
    }
    close(r.doneCh)
}()

and pkg/listen/proxy/proxy.go:251-254 treats a closed doneCh as a normal quit:

case <-p.renderer.Done():
    wsClient.Stop()
    p.renderer.Cleanup()
    return nil

So when the renderer dies at startup, hookdeck listen exits 0 within milliseconds having forwarded nothing, with the cause emitted only as a logrus line. This is the mechanism that made #333 invisible from the outside: no tunnel, no error, no non-zero exit.

Fix

Add Err() to the Renderer interface. The interactive renderer records the Bubble Tea failure; Proxy.Run returns it, and pkg/listen/listen.go:216-221 already converts that into stderr plus exit 1. A normal user quit (q / Ctrl-C) still returns nil.

Fixed in the v2.5.0 branch as part of #333.