feat(clients): unified stats vocabulary across every client + Moonlight comparison docs

One stat model everywhere (design/stats-unification.md): four measurement
points (capture/received/decoded/displayed), three stages that tile the
interval exactly, and a HUD that shows the addition explicitly —

  end-to-end 14.2 ms p50 · 19.8 p95 · capture→on-glass
  = host+network 9.8 + decode 2.1 + display 2.3

replacing each client's ad-hoc mix of overlapping absolutes (the Apple HUD's
three arrow lines that looked sequential but weren't), mean-vs-median decode
times (Windows/Linux), missing same-host-clock flags (Windows/Linux), and
three different names for the same capture→received measurement (probe's
"reassembled", Apple/Android's "client", Windows/Linux's post-decode "lat").

Per client: Apple threads receivedNs through the VT decode via the frame
refcon bit pattern so the decode stage exists at all (stage-1 fallback
honestly degrades to a capture→received headline); Windows carries
FrameTimes through the existing frame channel to the render thread and adds
e2e p50/p95 post-Present; Linux stamps received at AU pop and rides
decoded_ns on DecodedFrame to the paintable-set site; Android pairs receipt
stamps with MediaCodec output buffers via the codec's pts round-trip (JNI
stats array 14→16 doubles, indexes 0-13 unchanged). fps now uniformly counts
received AUs; lost/(received+lost) per window, hidden at zero.

docs-site gains "Understanding the Stats Overlay": what each line means, why
the equation only approximately sums (percentiles), and a line-by-line
Moonlight/Sunshine matrix — including that Moonlight has no end-to-end
number and its "network latency" is an ENet control RTT, so punktfunk's
headline must not be compared against any single Moonlight line.

Verified here: linux client + probe + core check/clippy/fmt green, android
native cargo-ndk arm64 check green. Pending: Windows CI + on-glass, swift
test on the mac, on-device Android.

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

clients/apple/Sources/PunktfunkClient/Session/StreamHUDView.swift

@@ -1,5 +1,7 @@
-// The streaming overlay HUD: mode + fps/throughput, the capture→client (and, under the stage-2
-// presenter, capture→present) latency lines, the platform input hint, and disconnect.
+// The streaming overlay HUD: mode + fps/throughput, the unified latency lines
+// (design/stats-unification.md — end-to-end headline + the stage equation under stage-2, the
+// capture→received headline under the stage-1 fallback), the loss counter, the platform input
+// hint, and disconnect.
 
 import PunktfunkKit
 import SwiftUI
@@ -18,24 +20,32 @@ struct StreamHUDView: View {
                 Text("\(connection.width)×\(connection.height)@\(connection.refreshHz)  \(model.fps) fps  \(model.mbps, specifier: "%.1f") Mb/s")
                     .font(.system(.caption, design: .monospaced))
             }
-            if model.latencyValid {
-                // Capture→client-receipt (skew-corrected); excludes the layer's decode+present —
-                // see LatencyMeter. "(same-host)" when the host didn't answer the skew handshake.
-                Text("capture→client \(model.latencyP50Ms, specifier: "%.1f")/\(model.latencyP95Ms, specifier: "%.1f") ms p50/p95\(model.latencySkewCorrected ? "" : " (same-host)")")
+            if model.endToEndValid {
+                // Stage-2: the end-to-end headline (capture→on-glass, measured directly, skew-
+                // corrected) — "(same-host clock)" when the host didn't answer the skew handshake.
+                Text("end-to-end \(model.endToEndP50Ms, specifier: "%.1f") ms p50 · \(model.endToEndP95Ms, specifier: "%.1f") p95 · capture→on-glass\(model.endToEndSkewCorrected ? "" : " (same-host clock)")")
+                    .font(.system(.caption2, design: .monospaced))
+                    .foregroundStyle(.secondary)
+                // The equation: the three stages tiling the headline interval (per-window p50s —
+                // they only approximately sum to the directly-measured total).
+                if model.hostNetworkValid && model.decodeValid && model.displayValid {
+                    Text("= host+network \(model.hostNetworkP50Ms, specifier: "%.1f") + decode \(model.decodeP50Ms, specifier: "%.1f") + display \(model.displayP50Ms, specifier: "%.1f")")
+                        .font(.system(.caption2, design: .monospaced))
+                        .foregroundStyle(.secondary)
+                }
+            } else if model.hostNetworkValid {
+                // Stage-1 fallback presenter: the layer decodes + presents internally with no
+                // per-frame stamp, so the honest headline ends at receipt — and there is no
+                // equation line (host+network is the whole measured interval).
+                Text("capture→received \(model.hostNetworkP50Ms, specifier: "%.1f") ms p50 · \(model.hostNetworkP95Ms, specifier: "%.1f") p95\(model.hostNetworkSkewCorrected ? "" : " (same-host clock)")")
                     .font(.system(.caption2, design: .monospaced))
                     .foregroundStyle(.secondary)
             }
-            if model.presentLatencyValid {
-                // Capture→present (glass-to-glass, modulo host render→capture) — stage-2 presenter
-                // only; stage-1's layer presents internally with no per-frame stamp.
-                Text("capture→present \(model.presentLatencyP50Ms, specifier: "%.1f")/\(model.presentLatencyP95Ms, specifier: "%.1f") ms p50/p95\(model.presentLatencySkewCorrected ? "" : " (same-host)")")
-                    .font(.system(.caption2, design: .monospaced))
-                    .foregroundStyle(.secondary)
-            }
-            if model.presentTailValid {
-                // Decode→present (the client-local "present tail": ring wait + render + vsync) —
-                // the term the stage-2 presenter shortens; no skew applies (one clock).
-                Text("decode→present \(model.presentTailP50Ms, specifier: "%.1f")/\(model.presentTailP95Ms, specifier: "%.1f") ms p50/p95")
+            if model.lostFrames > 0 {
+                // Unrecoverable network drops this window; hidden while the link is clean.
+                // String(format:) rather than specifier interpolation: the literal % would
+                // otherwise land in the LocalizedStringKey's format string as a bogus conversion.
+                Text(String(format: "lost %d (%.1f%%)", model.lostFrames, model.lostPct))
                     .font(.system(.caption2, design: .monospaced))
                     .foregroundStyle(.secondary)
             }