iris: FrameReport CPU/GPU split, force-gles backend switch, iris-scroll.sh rig

Splits each frame sample at queue.submit into redraw-to-submit (iris's own
CPU work) and submit-to-after-present (driver/GPU wait), so RUST.md's I5
"where does iris's frame time go" question can be answered with a number
per half instead of a single total. Adds a force-gles Cargo feature that
switches the Android wgpu::Instance from Backends::PRIMARY to Backends::GL
at compile time (no runtime env-var path exists into an already-launched
Android process on this machine), for isolating SwiftShader-Vulkan vs.
GLES/virgl as the software-mode gap's cause. app/iris-scroll.sh extracts
transcript-bench.sh's exact 24-swipe/6-cycle gesture loop for iris's own
demo app, which transcript-bench.sh cannot drive directly since it opens a
session through the Compose app's own UI.

Verification (this pass, on a disk-pressure-limited host running low on
space): cargo fmt --all clean, no diff. cargo clippy --workspace
--all-targets: no warnings from this diff (pre-existing future-incompat
notices from wgpu/winit/naga only). cargo test --workspace and cargo ndk
for iris-android-app --features transcript-screen were verified clean by
the previous pass on this identical diff (fmt/clippy/test/ndk all clean,
per that pass's own report); not re-run here because the host's disk was
93% full and a concurrent ai-server rebuild (stable toolchain moved to
1.98.1, rebuilding aws-lc-sys from scratch) had driven I/O pressure to
~60%, so a repeat cargo test --workspace sat 50+ minutes doing no useful
work and was stopped rather than left to make the disk situation worse.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/iris-scroll.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+# RUST.md's I5 "Where iris's frame time goes" pass (2026-09-05). The same
+# 24-swipe/6-cycle loop as transcript-bench.sh's, extracted for iris's own
+# demo app -- transcript-bench.sh itself is Compose-specific (opens by
+# session title through the Compose app's own UI) and cannot be called
+# directly against dev.iris.android.demo.
+#
+# MUST be run from inside this checkout (not /tmp): ui-trace/adb pick which
+# emulator to target from the current directory's basename (the
+# per-checkout-AVD rule), and a previous pass lost two attempts to a `cd`
+# into /tmp that made this resolve to a nonexistent "tmp" checkout.
+set -eu
+cd "$(dirname "$0")"
+. ./android-env.sh >/dev/null 2>&1
+
+cycles=${1:-6}
+
+ui-trace record -d 3000 --do "tap 'Reset frame report'" -o /tmp/iris-bench-reset.txt >/dev/null
+adb logcat -c
+
+DO=""
+i=0
+while [ "$i" -lt "$cycles" ]; do
+    DO="$DO --do 'swipe 540 700 540 1600 200' --do 'wait 500'"
+    DO="$DO --do 'swipe 540 700 540 1600 200' --do 'wait 500'"
+    DO="$DO --do 'swipe 540 1600 540 700 200' --do 'wait 500'"
+    DO="$DO --do 'swipe 540 1600 540 700 200' --do 'wait 500'"
+    i=$((i + 1))
+done
+eval ui-trace record -d $((cycles * 16000 + 20000)) $DO -o /tmp/iris-bench-scroll.txt >/dev/null
+
+ui-trace record -d 3000 --do "tap 'Frame report'" -o /tmp/iris-bench-report.txt >/dev/null
+sleep 1
+adb logcat -d -s iris-android-app:I | grep "iris frame report:"