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/Cargo.toml

@@ -0,0 +1,125 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2021"
+rust-version = "1.66"
+name = "ndk"
+version = "0.9.0"
+authors = ["The Rust Mobile contributors"]
+description = "Safe Rust bindings to the Android NDK"
+homepage = "https://github.com/rust-mobile/ndk"
+documentation = "https://docs.rs/ndk"
+readme = "README.md"
+keywords = [
+    "android",
+    "ndk",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-mobile/ndk"
+
+[package.metadata.docs.rs]
+features = [
+    "jni",
+    "all",
+]
+rustdoc-args = [
+    "--cfg",
+    "docsrs",
+]
+targets = [
+    "aarch64-linux-android",
+    "armv7-linux-androideabi",
+    "i686-linux-android",
+    "x86_64-linux-android",
+]
+
+[dependencies.bitflags]
+version = "2.4"
+
+[dependencies.ffi]
+version = "0.6.0"
+package = "ndk-sys"
+
+[dependencies.jni]
+version = "0.21"
+optional = true
+
+[dependencies.jni-sys]
+version = "0.3"
+
+[dependencies.log]
+version = "0.4.6"
+
+[dependencies.num_enum]
+version = "0.7"
+
+[dependencies.rwh_04]
+version = "0.4"
+optional = true
+package = "raw-window-handle"
+
+[dependencies.rwh_05]
+version = "0.5"
+optional = true
+package = "raw-window-handle"
+
+[dependencies.rwh_06]
+version = "0.6"
+optional = true
+package = "raw-window-handle"
+
+[dependencies.thiserror]
+version = "1.0.23"
+
+[dev-dependencies.libc]
+version = "0.2.3"
+
+[features]
+all = [
+    "audio",
+    "bitmap",
+    "media",
+    "nativewindow",
+    "sync",
+    "api-level-33",
+    "rwh_04",
+    "rwh_05",
+    "rwh_06",
+]
+api-level-23 = []
+api-level-24 = ["api-level-23"]
+api-level-25 = ["api-level-24"]
+api-level-26 = ["api-level-25"]
+api-level-27 = ["api-level-26"]
+api-level-28 = ["api-level-27"]
+api-level-29 = ["api-level-28"]
+api-level-30 = ["api-level-29"]
+api-level-31 = ["api-level-30"]
+api-level-32 = ["api-level-31"]
+api-level-33 = ["api-level-32"]
+audio = [
+    "ffi/audio",
+    "api-level-26",
+]
+bitmap = ["ffi/bitmap"]
+default = ["rwh_06"]
+media = ["ffi/media"]
+nativewindow = ["ffi/nativewindow"]
+sync = [
+    "ffi/sync",
+    "api-level-26",
+]
+test = [
+    "ffi/test",
+    "jni",
+    "all",
+]