fix(player): make Android native video actually visible, and usable

DR-172 reverted native video to opt-in after it shipped as audio with no
picture, naming the compositing as the suspect. The compositing was fine. Five
separate defects sat between ExoPlayer and the screen, each able to produce that
exact symptom on its own, and each invisible to the others.

DR-185 — the app shell painted over the surface. app.css clears the page's
opaque layers through three selectors, one of which targets `[data-app-shell]`,
an attribute NO component has ever set, in any commit. The shell paints
--color-background across the whole viewport and VideoPlayer stacks above it, so
the WebView composited opaque no matter what else was cleared. Invisible three
ways over: the CSS is valid, the selector is plausible, and a rule matching
nothing looks exactly like a rule matching something already transparent.

DR-182 — nothing could lift the poster card. Every markMediaReady() call site is
an HTML5 <video> event, and the native branch renders no element, so the black
title card covered the surface for the entire session. The first fix hooked
`player://position-update` / `player://state-changed`; those channels are never
emitted by the backend, so it passed a test that fired them by hand and did
nothing on a device. Driven from the player store now, as the seek bar already
was.

DR-183 — the JS bridges raced the page load. Installed 500ms after onCreate by
walking the view tree, while WebView binds injected objects at page-load time,
and the identity guard then declined to re-inject forever. setTransparent(true)
could never arrive. Installed from WryActivity.onWebViewCreate instead, which
wry calls immediately before the first loadUrl.

DR-184 — the SurfaceView was never detached. detachVideoSurface had no callers
anywhere, mirroring the DR-151 defect: every native video left its surface
parented to the content view and the next one stacked another beneath it.

DR-191 — the overlay stopped repainting. Incremental damage (the clock's text,
the control bar's opacity) never reached the screen while structural changes did,
so the progress bar froze, the controls would not fade, and the play overlay
appeared to work because it is added and removed from the DOM. Driven from the
Activity via postInvalidateOnAnimation while compositing is on.

Two UI defects only this path could reveal came with them: isPlaying froze at
its initial value, leaving the play overlay dimming and covering the video
(DR-186), and the control bar's auto-hide was armed solely by mousemove, which a
touchscreen never fires (DR-189). Immersive mode now applies on entering the
player rather than only via the fullscreen button (DR-187).

Verified on a device (Honor ROD2-W09, Android 16): logcat carries
`WebView transparent = true` and `Marking media ready` with video on screen —
the pair DR-172 went looking for and could not find — and skip, seek, rotation
and subtitle rendering were exercised by hand.

The default stays OFF (DR-188). Turning it on surfaced a further unverified
sub-path: returning from background audio is HTML5-only, so playback stays dead
(DR-190, proposed). Shipping it would have repeated DR-161 exactly — a verified
sub-path made default over an unverified one.

docs/specs/android-native-video-spike.md

@@ -1,8 +1,12 @@
 # Spec: Android native video — transparent-webview spike
 
-**Status:** Spike succeeded — native video confirmed working on a physical
-device (2026-08-11) with `experimentalNativeVideo` on. Shipped behind that flag,
-default off. Branch `feat/android-native-video`.
+**Status:** Spike succeeded (2026-08-11); shipped behind `experimentalNativeVideo`,
+default off. Flipping that default shipped **audio with no picture** and was
+reverted (DR-172). Three defects behind that have since been fixed — DR-182
+(nothing on the native path could lift the poster overlay), DR-183 (the JS
+bridges raced the page load), DR-184 (the SurfaceView was never detached).
+Branch `fix/android-native-video-visible`. **The default stays off until the
+device criteria below are green.**
 
 **The spike's central question is answered: yes.** A `SurfaceView` *can* be
 composited behind a transparent Tauri WebView on Android. Nothing upstream
@@ -227,6 +231,9 @@ The spike is **complete** when one of these is true:
 - [x] `experimentalNativeVideo` off → behaviour byte-identical to today. Guarded by `adapterSelection.test.ts`, which asserts the flag-off case forces HTML5 even when Rust reports native.
 - [x] `webviewAudio.ts` no longer inspects `navigator.userAgent`; the platform's audio backend is read from Rust (`player_get_capabilities` → `usesWebviewAudio`).
 - [x] `experimentalNativeVideo` on → video plays via ExoPlayer, correctly positioned, on a physical device (2026-08-11). The surface reaches the hierarchy and is visible through the transparent WebView — the whole point of the spike.
+- [x] The poster/title card comes down on the native path. It never could: every `markMediaReady()` call site is a `<video>` element event and the native branch renders no element, so an opaque `bg-black` overlay covered the ExoPlayer surface for the whole session. See DR-182; guarded by `mediaReady.test.ts` (UT-184) and `VideoPlayer.nativeReveal.test.ts` (UT-185), the latter written failing first.
+- [x] The `AndroidVideoSurface` bridge is installed before the page that calls it loads, via `WryActivity.onWebViewCreate` instead of a 500 ms tree walk, and a missing bridge now logs an error instead of no-oping. See DR-183.
+- [x] The SurfaceView is detached when video stops, instead of accumulating one leaked view per native video. See DR-184.
 - [ ] Seek, audio-track switch and subtitle selection exercised through `NativePlayerAdapter`. Playback is confirmed; these individual controls are not yet each verified on the native path.
 - [ ] No artefacts on rotation, background/foreground, or **mini-player transition** — the last is the one case the fullscreen assumption does not cover, so it is the likeliest place to find a problem.
 - [ ] `adb shell dumpsys media.metrics` (or logcat) confirms a hardware decoder is in use. Plausible but unmeasured — do not claim the MediaCodec win until this is read.
@@ -238,9 +245,26 @@ The spike is **complete** when one of these is true:
 - [ ] `nativeAdapter.ts:11-14` no longer cites tauri#10152.
 
 Either way:
-- [x] `bun run check` (0 errors), `bun run test` (892 passed), `bun run check:boundary` pass.
+- [x] `bun run check` (0 errors), `bun run test` (997 passed), `bun run check:boundary` pass.
 - [x] `cargo fmt` / `cargo clippy` clean (no new warnings); `cargo test` passes (603 lib + 7 doc).
 
+### Why the 2026-08-11 verification and DR-172 do not contradict each other
+
+The spike was reported working on device; the same path then shipped as audio
+with no picture. Both are consistent with DR-182: the poster overlay is drawn
+only while `isMediaReady` is false, and the native path has no way to set it, so
+what the surface shows depends entirely on **whether that overlay is on screen**
+— not on whether compositing works. Any run that reached the player through a
+path leaving `isMediaReady` already true (a handoff return, a re-render, a
+session that had previously played on the HTML5 path) shows video; a cold start
+into the native path never does. That is also why DR-172 read the symptom as a
+compositing failure: on screen the two are identical, and the one piece of
+evidence separating them — `WebView transparent = true` never being logged —
+points at DR-183 rather than at the compositing itself.
+
+**This reasoning is not yet device-confirmed.** It explains the reports and is
+backed by the code, but the criteria above are what settle it.
+
 > Note: this environment has no host WebKitGTK dev packages, no Android SDK and
 > no `bun`, so all of the above were run inside the CI builder image
 > (`gitea.tourolle.paris/dtourolle/jellytau-builder:latest`). On Fedora the bind