Import fails with "stream did not contain valid UTF-8" on Android 16, even for a byte-identical round-trip of an already-working deck

### Checked for duplicates?

- [x] This issue is not a duplicate

### Does it also happen in the desktop version?

- [x] This bug does not occur in the latest version of Anki Desktop

### What are the steps to reproduce this bug?

1. Export a deck from AnkiDroid on this device (this file imports fine — control case).
2. On a separate machine, install `anki==25.9.2` via pip. It reports `buildhash: 3890e12c` — the exact same core commit as this device's bundled backend.
3. Using that pip package, import the file from step 1 with Collection.import_anki_package(), then immediately export it again with Collection.export_anki_package(), with no content changes (with_scheduling=True, with_deck_configs=True, with_media=True, legacy=False).
4. Transfer the resulting file back to the device and import it via Menu → Import (not "Open with" — ruling out share-intent/cache-copy timing issues).

Also tried with legacy=True on export (produces collection.anki21 instead of collection.anki21b) — same error. CSV import of equivalent content works fine on the same device, same session.

### Expected behaviour

Expected: import succeeds, since the file is a scheduling/content-preserving round-trip of a file that already imports successfully on this device, produced by the exact same core commit (3890e12c) as the device's bundled backend.

Actual: fails with the same error as any other freshly-generated .apkg:
500: Failed to read 'data/user/0/com.ichi2.anki/cache/.apkg': stream did not contain valid UTF-8

Since the backend commit is identical between the working and failing files, and content/schema-level checks all matched (zip entry list, `meta` version bytes, decompressed collection.anki21b SQLite schema/content), this looks specific to how AnkiDroid's Kotlin/JNI layer reads the file into the Rust core on this Android version/device rather than a core-library or file-content issue. Android 16 is a very recent release, so a scoped-storage/file-access change there seems like a plausible lead.

### Debug info

```text
AnkiDroid Version = 2.24.0 (ebcf8e0e34921628b9b8a496c66ffd4adbb3705f)
Backend Version = 0.1.64-anki25.09.2 (25.09.2 3890e12c9e48c028c3f12aa58cb64bd9f8895e30)
Android Version = 16 (SDK 36)
ProductFlavor = play
Device Info = samsung | samsung | gts10fepwifi | gts10fepwifixx | SM-X620 | s5e8855
WebView Info = [com.google.android.webview | 787118103]: Mozilla/5.0 (Linux; Android 16; SM-X620 Build/BP4A.251205.006; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/150.0.7871.181 Safari/537.36
ACRA UUID = 673d35c1-959b-4177-a8b1-effe863b711b
FSRS = 5.1.0 (Enabled: true)
Crash Reports Enabled = true
```

### (Optional) Anything else you want to share?

Happy to provide any of the generated test .apkg files or run further diagnostics if useful.

### Research

- [x] I have checked the [manual](https://docs.ankidroid.org/) and the [FAQ](https://github.com/ankidroid/Anki-Android/wiki/FAQ) and could not find a solution to my issue
- [ ] (Optional) I have confirmed the issue is not resolved in the latest alpha release ([instructions](https://docs.ankidroid.org/manual.html#betaTesting))