feat(clients/android): OnFrameRendered display stage — HUD headline becomes capture→displayed

The long-deferred Android display stage (design/stats-unification.md; plan 4.1 of
design/client-parity-and-network-resilience.md): AMediaCodec_setOnFrameRenderedCallback
(API 26, under the minSdk-28 floor ⇒ hard-linked via ndk-sys) reports SurfaceFlinger's
per-frame render timestamp, giving the HUD the spec's `display` = decoded→displayed term
and the directly-measured capture→displayed end-to-end headline on both decode loops.
Falls back per spec to the v1 capture→decoded endpoint on any window without render
callbacks (the platform may drop them under load), and to it permanently if registration
is refused.

- The render timestamp arrives on CLOCK_MONOTONIC; it's re-based onto CLOCK_REALTIME
  against monotonic-now at callback time, which also cancels the (batchable) callback
  delivery lag.
- The `ndk` crate exposes neither the callback nor the codec pointer needed to bind it
  raw, so the workspace pins `ndk` 0.9.0 to a vendored copy (clients/android/native/
  vendor/ndk) whose ONLY change makes MediaCodec::as_ptr public — the "as_ptr patch".
  Workspace-excluded so host builds never compile it; drop when upstream exposes either.
- nativeVideoStats grows to 26 doubles (22–25: dispValid, displayP50, e2eDispP50/P95;
  0–21 unchanged for older readers); StatsOverlay moves headline endpoint + equation
  together so the equation always tiles the headline interval.

Verified: host cargo check/test/clippy, aarch64-linux-android check/clippy, Kotlin
app+kit+tests compile, roborazzi HUD render shows the full 4-term equation. Device
verification rides plan 4.2's phone A/B.

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

Cargo.toml

@@ -19,7 +19,19 @@ members = [
     "tools/loss-harness",
 ]
 # Standalone PoC (built on its own; pulls usbip/tokio/libusb we don't want in the workspace).
-exclude = ["packaging/linux/steam-deck-gadget/usbip-poc"]
+# The vendored `ndk` is a [patch.crates-io] source, not a member: it only compiles for the
+# `*-linux-android` targets, so workspace membership would break host `cargo build --workspace`.
+exclude = [
+    "packaging/linux/steam-deck-gadget/usbip-poc",
+    "clients/android/native/vendor/ndk",
+]
+
+# ndk 0.9.0 verbatim from crates.io plus ONE visibility change: `MediaCodec::as_ptr` made public
+# (upstream keeps it private and exposes no frame-rendered binding), so the Android client can
+# call `AMediaCodec_setOnFrameRenderedCallback` via ndk-sys for the HUD's `display` stage
+# (design/stats-unification.md). Drop the patch when upstream exposes the pointer or the callback.
+[patch.crates-io]
+ndk = { path = "clients/android/native/vendor/ndk" }
 
 [workspace.package]
 version = "0.8.4"