This commit makes two changes to the web client auth flow error
handling:
1. Properly passes back the error code from the noise request from
the localapi. Previously we were using io.Copy, which was always
setting a 200 response status code.
2. Clean up web client browser sessions on any /wait endpoint error.
This avoids the user getting in a stuck state if something goes
wrong with their auth path.
Updates tailscale/corp#14335
Signed-off-by: Sonia Appasamy <sonia@tailscale.com>
68da15516f