feat(clients): host/network split in every stats HUD (stats phase 2, client side)

Consumes the 0xCF host-timing plane (449a67c) on all four GUI clients: each
keeps a bounded pending ring of receipt samples keyed by pts, matches the
host's per-AU capture→sent reports against it, and the HUD equation becomes

  = host 3.1 + network 6.7 + decode 2.1 + display 2.3

falling back to the combined `= host+network …` term whenever no timing
matched the window (old host / datagram loss) — same total, one split
fewer, never a misleading zero. Apple additionally gains the split as the
only equation line under the stage-1 fallback presenter (receipt is
presenter-independent), a `nextHostTiming` wrapper with its own plane lock,
and a unit-tested `HostNetworkSplitter`; Android extends the JNI stats
array 16→18 doubles (0–15 unchanged); Windows/Linux thread the split
through `Stats` into the HUD and the headless/debug logs.

Docs updated: design/stats-unification.md Phase 2 → implemented (wire
format, fallback semantics), and the docs-site matrix's Sunshine "Host
processing latency" row is now a direct match (ours includes the paced
send; avg vs p50).

Verified here: linux client clippy -D warnings green on the live tree,
windows stub check + hand-verified diff, android cargo-ndk arm64 check
green, apple loopback test extended (needs the rebuilt xcframework + swift
test on the mac). On-glass: pending on all platforms.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/windows/src/main.rs

@@ -238,6 +238,18 @@ fn run_headless_cli(args: &[String], identity: (String, String)) {
                 session::SessionEvent::Connected {
                     mode, fingerprint, ..
                 } => tracing::info!(?mode, fp = %trust::hex(&fingerprint), "connected"),
+                // With per-AU 0xCF host timings the combined host+network stage splits into
+                // host (capture→sent on the host) + net; an old host emits none → combined only.
+                session::SessionEvent::Stats(s) if s.split => tracing::info!(
+                    fps = format!("{:.0}", s.fps),
+                    mbps = format!("{:.1}", s.mbps),
+                    decode_p50_ms = format!("{:.2}", s.decode_ms),
+                    hostnet_p50_ms = format!("{:.2}", s.hostnet_ms),
+                    host_p50_ms = format!("{:.2}", s.host_ms),
+                    net_p50_ms = format!("{:.2}", s.net_ms),
+                    frames_seen,
+                    "stats"
+                ),
                 session::SessionEvent::Stats(s) => tracing::info!(
                     fps = format!("{:.0}", s.fps),
                     mbps = format!("{:.1}", s.mbps),