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/android/kit/src/main/kotlin/io/unom/punktfunk/kit/NativeBridge.kt

@@ -105,14 +105,17 @@ object NativeBridge {
 
     /**
      * Drain ~1 s of live decode stats for the on-stream HUD, or `null` when no decode thread runs.
-     * Returns 16 doubles (unified stats spec, `design/stats-unification.md`):
+     * Returns 18 doubles (unified stats spec, `design/stats-unification.md`):
      * `[fps, mbps, e2eP50Ms, e2eP95Ms, latValid, skewCorrected, width, height, refreshHz, framesLost,
-     * bitDepth, colorPrimaries, colorTransfer, chromaFormatIdc, hostNetP50Ms, decodeP50Ms]`
+     * bitDepth, colorPrimaries, colorTransfer, chromaFormatIdc, hostNetP50Ms, decodeP50Ms, hostP50Ms,
+     * netP50Ms]`
      * (the two flags are 1.0/0.0; indexes 2/3 are the end-to-end capture→decoded headline; 10–13
      * describe the negotiated video feed — bit depth 8/10, CICP primaries/transfer, and the HEVC
      * chroma_format_idc 1=4:2:0 / 3=4:4:4; 14/15 are the stage p50s tiling the headline —
-     * `host+network` = capture→received, `decode` = received→decoded). Poll ~1 Hz; each call
-     * resets the measurement window.
+     * `host+network` = capture→received, `decode` = received→decoded; 16/17 split the
+     * `host+network` term via the host's per-AU 0xCF timings — `host` = the host's capture→sent,
+     * `network` = the remainder — both 0.0 when no timing matched this window, i.e. an old host).
+     * Poll ~1 Hz; each call resets the measurement window.
      */
     external fun nativeVideoStats(handle: Long): DoubleArray?