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>

clients/android/native/vendor/ndk/README.md

@@ -0,0 +1,21 @@
+[![ci](https://github.com/rust-mobile/ndk/actions/workflows/rust.yml/badge.svg)](https://github.com/rust-mobile/ndk/actions/workflows/rust.yml) ![MIT license](https://img.shields.io/badge/License-MIT-green.svg) ![APACHE2 license](https://img.shields.io/badge/License-APACHE2-green.svg)
+
+Rust bindings to the [Android NDK](https://developer.android.com/ndk)
+
+Name | Description | Badges
+--- | --- | ---
+[`ndk-sys`](./ndk-sys) | Raw FFI bindings to the NDK | [![crates.io](https://img.shields.io/crates/v/ndk-sys.svg)](https://crates.io/crates/ndk-sys) [![Docs](https://docs.rs/ndk-sys/badge.svg)](https://docs.rs/ndk-sys) [![MSRV](https://img.shields.io/badge/rustc-1.60.0+-ab6000.svg)](https://blog.rust-lang.org/2022/04/07/Rust-1.60.0.html)
+[`ndk`](./ndk) | Safe abstraction of the bindings | [![crates.io](https://img.shields.io/crates/v/ndk.svg)](https://crates.io/crates/ndk) [![Docs](https://docs.rs/ndk/badge.svg)](https://docs.rs/ndk) [![MSRV](https://img.shields.io/badge/rustc-1.64.0+-ab6000.svg)](https://blog.rust-lang.org/2022/09/22/Rust-1.64.0.html)
+
+See these [`ndk-examples`](https://github.com/rust-mobile/cargo-apk/tree/main/examples/examples) and these [`rust-android-examples`](https://github.com/rust-mobile/rust-android-examples) for examples using the NDK.
+
+> [!IMPORTANT]
+> This repository was recently [modularized](https://github.com/rust-mobile/ndk/issues/372) and the following crates were split into separate repositories:
+>
+> Crate | New Location | Notes
+> ------|--------------|------
+> ndk-context | https://github.com/rust-mobile/ndk-context |
+> ndk-glue | https://github.com/rust-mobile/ndk-glue | ⛔ _deprecated_ - see [android-activity](https://github.com/rust-mobile/android-activity)
+> ndk-macro | https://github.com/rust-mobile/ndk-glue | ⛔ _deprecated_ - see [android-activity](https://github.com/rust-mobile/android-activity)
+> ndk-build | https://github.com/rust-mobile/cargo-apk | ⛔ _deprecated_ - see [xbuild](https://github.com/rust-mobile/xbuild)
+> cargo-apk | https://github.com/rust-mobile/cargo-apk | ⛔ _deprecated_ - see [xbuild](https://github.com/rust-mobile/xbuild)