iris: add an android-view backend beside winit (I2, part 1)

Relocates the platform-neutral halves of the winit `default` backend
(WidgetState, CursorState/sense, Tasks, Selector/Selectable's focus
handling) into shared crate-root modules so both backends can use them
without duplication, generalizes Tasks' redraw nudge behind a
RequestRedraw trait instead of a concrete winit::window::Window, and
adds iris/src/android/: a second backend on android-view's ViewPeer --
wgpu on the view's surface, touch as a mouse-like cursor, an
InputConnection bridge onto TextEdit (I1's parley editor), and a
window-insets side channel since android-view has no hook for it.
winit's own Android support pulls in android-activity without a
selected backend feature, so `default`/`android` are now target-gated
rather than both compiled in; confirmed by cross-compiling before this
split (cargo ndk failed inside android-activity) and after (clean).

Host build/clippy/fmt/tests and the android (x86_64, API 26)
cross-compile of the iris crate are all clean; the winit tabs example
still renders via run-headless.sh. Not yet exercised: an actual
android-app crate and Gradle shell to run this on the emulator -- next
in RUST.md's I2.

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

iris/Cargo.toml

@@ -10,13 +10,36 @@ iris-core = { workspace = true }
 iris-macro = { workspace = true }
 parley = { workspace = true }
 swash = { workspace = true }
-winit = { workspace = true }
-arboard = { workspace = true, features = ["wayland-data-control"] }
 pollster = { workspace = true }
 wgpu = { workspace = true }
 image = { workspace = true }
 tokio = { workspace = true, features = ["sync", "rt", "rt-multi-thread"] }
 
+# winit everywhere except Android; android-view (below) is what stands in
+# for it there. Both backends live in this crate (see `src/android/mod.rs`'s
+# doc comment) but are never compiled together: winit's own Android support
+# pulls in `android-activity`, which panics at compile time unless one of
+# its own backend features is picked, and picking one is exactly what
+# `iris-core` was kept free of (RUST.md's I0b). Confirmed by trying it
+# 2026-09-05: `cargo ndk -t x86_64 -P 26 build -p iris` failed inside
+# `android-activity` itself with "Either game-activity or native-activity
+# must be enabled" before this split existed.
+[target.'cfg(not(target_os = "android"))'.dependencies]
+winit = { workspace = true }
+arboard = { workspace = true, features = ["wayland-data-control"] }
+
+# Pinned to the exact commit RUST.md's E1 (2026-09-04) measured on this
+# emulator -- real Vulkan rendering, a working `InputConnection`, and the
+# accesskit-detach abort, all against this rev specifically. Advancing it
+# wants re-running E1's checks, the same reason the nightly toolchain pin
+# is dated rather than floating.
+[target.'cfg(target_os = "android")'.dependencies]
+android-view = { git = "https://github.com/rust-mobile/android-view.git", rev = "bec6c62a96cef8239b0fd7fedeef9b184d02e3a1" }
+# Not re-exported by android-view (only `jni` and `ndk` are), and needed
+# for `android/insets.rs`'s own id -> state map -- the same reason
+# android-view's own `PEER_MAP` carries one.
+send_wrapper = "0.6.0"
+
 [dev-dependencies]
 tokio = { workspace = true, features = ["sync", "rt", "rt-multi-thread", "time"] }