v0.6.5 — surface CC2 'LAN Only' requirement

Fixed

• CC2 connect now surfaces a clear error when the printer's HTTP API is
  unreachable instead of leaking a raw httpx.ConnectError. The CC2
  gates its local API behind "LAN Only" mode — with it off, the
  printer works through Elegoo's cloud and leaves port 80 closed, so the
  serial-number bootstrap fails even though MQTT :1883 answers. The
  error now says exactly that and names the setting to change. (Reported
  by a user on firmware 02.00.02.00 whose connection worked the moment
  they enabled LAN Only.)

Documentation

• README and docs/PROTOCOL.md now document that "LAN Only" mode must
  be enabled on the CC2 for local control, and note that firmware
  02.00.02.00 is a lockdown release (removes SSH, blocks downgrades)
  with a community repacked v01.03.02.51 available if needed.