The broadcast fanout, supervisor-facing listener bind, accept loop, and
per-viewer drain were all sitting inside host/wayland.rs even though
none of it is Wayland-specific. Move them to host/serve.rs so the X11
backend can share the same serving layer with a one-line constructor
call instead of copy-pasting (and drifting on) the fanout code.
No behavior change. Wayland's CaptureHandle now wraps a serve::Serve
instead of owning the listener/reader/server fields directly; gst
pipeline construction is unchanged. connect_to_capture moves alongside
Serve since it pairs with it.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
