Backports the HeaderEntry / HttpProxyRequest / HttpProxyResponse messages
and the corresponding union tags from upstream rustdesk/hbb_common
@87b11a7 onto the OSS server's pinned commit @83419b6 — wire-compatible
with the client-side encoder in rustdesk's src/common.rs::tcp_proxy_request.
Cherry-pick over a full submodule bump because the upstream commit pulls
newer transitive deps (notably tokio) that risk breaking axum 0.5 in the
hbbs HTTP layer.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>