Implement QUIC networking for wrsrvd (server) and wrclient (client) using
quinn over rustls with self-signed certificates. Three logical channels:
control (bidirectional), display (server->client unidirectional), and
input (client->server unidirectional).
Server runs tokio in a background thread, communicating with the compositor
via std::sync::mpsc channels. Client exposes an async connect() API that
returns a ServerConnection with methods for sending input and receiving
frames.
Key design note: quinn streams are lazily materialized -- accept_bi/
accept_uni on the peer won't resolve until data is written. The handshake
protocol accounts for this by having each side write immediately after
opening streams.
Restructure wrsrvd to support two backends: a headless PixmanRenderer
(default) for running without a display server, and the existing Winit
backend (via --backend winit). The render logic is split into per-backend
modules, and the old render.rs is removed.
