fix(player): make native Android video opt-in again — it shipped as audio with no picture

DR-161 flipped experimentalNativeVideo on by default so picture-in-picture could
shrink a real video surface. On a device that shipped sound with a blank screen.

The decode path was never at fault. Logcat shows ExoPlayer running and feeding a
live SurfaceView with an active BufferQueue. The compositing was: the SurfaceView
sits behind the WebView, and the step that clears the opaque layers above it
never took effect — `WebView transparent = false` is logged, `= true` never
appears. The video was rendering correctly the whole time, behind an opaque page.

This is precisely the defect the flag existed to contain;
VideoPlayer.scrubRegression.test.ts had already recorded that "the native
SurfaceView has never been visible through the webview". Enabling it by default
shipped a verified decode path on top of an unverified display path.

Reverting costs nothing that matters: PiP does not depend on it — DR-160 drives
PiP from the WebView <video> — and working video outranks PiP showing a native
surface. The flag stays in Settings, now described as incomplete rather than as a
performance win, so anyone helping test it still can.

Fixing the compositing is the prerequisite for trying this default again (DR-172).

src/lib/stores/nativeVideo.ts

@@ -27,26 +27,32 @@ const STORAGE_KEY = "jellytau-experimental-native-video";
 const NATIVE_VIDEO_ATTR = "data-native-video";
 
 /**
- * Whether the native path is on, defaulting to **on** when the user has never
- * chosen.
+ * Whether the native path is on. **Off** unless the user turned it on.
  *
- * It shipped defaulting to off while the native path was a spike. It is now the
- * default because picture-in-picture is built on it: PiP shrinks the *Activity*,
- * so it needs a real video surface behind the WebView to show, and on the HTML5
- * path there is nothing for it to shrink into but the UI itself (DR-160).
+ * DR-161 briefly made this default to on, so picture-in-picture could shrink a
+ * real video surface. On a device that shipped as **audio with no picture**:
+ * ExoPlayer decoded correctly and fed its SurfaceView, but the SurfaceView sits
+ * *behind* the WebView and the compositing that clears the opaque layers above it
+ * never took effect — logcat showed `WebView transparent = false` and never
+ * `= true`. So the video was rendering the whole time, behind the page.
+ *
+ * That is the defect the flag existed to contain, and it is why the default is
+ * back off: video working matters more than PiP showing the native surface, and
+ * PiP still works without it via the HTML5 path (DR-160). Native video remains
+ * available in Settings for anyone testing it.
  *
  * An explicit stored choice still wins in both directions, so anyone who turned
- * it off keeps it off.
+ * it on keeps it on.
+ *
+ * TRACES: UR-003, UR-004 | DR-172
  */
 function load(): boolean {
-  if (typeof localStorage === "undefined") return true;
+  if (typeof localStorage === "undefined") return false;
   try {
-    const stored = localStorage.getItem(STORAGE_KEY);
-    return stored === null ? true : stored === "true";
+    return localStorage.getItem(STORAGE_KEY) === "true";
   } catch {
-    // Private-mode / disabled storage — no stored choice is readable, so this is
-    // the same case as "never chosen".
-    return true;
+    // Private-mode / disabled storage — default to the safe (HTML5) path.
+    return false;
   }
 }
 
@@ -74,8 +80,8 @@ function createExperimentalNativeVideoStore() {
 }
 
 /**
- * User opt-out for the native Android video path. **Defaults to on** since
- * DR-161 — see `load()`. The name still says "experimental" because the flag
+ * User opt-in for the native Android video path. **Defaults to off** again since
+ * DR-172 — see `load()`. The name says "experimental" because the flag
  * remains a suppressor of Rust's backend choice, not a promoter of it.
  */
 export const experimentalNativeVideo = createExperimentalNativeVideoStore();