Address several gaps in the app export feature (#1132):
- Bundle shared-library APKs and OBB/patch files, preserving their
relative layout (libraries/<pkg>/ and Android/obb/<pkg>/).
- Fall back to the installed app's on-device APKs when the cached
download was cleared (e.g. auto-deleted after install), guarded by an
exact version match so a different installed version is never exported.
- Guard against the download row being replaced by a manual download of
another version between enqueue and execution.
- Fail (and delete the partial/empty document) instead of reporting
success when there is nothing to bundle or an error occurs.
- Store entries uncompressed and use larger buffers, so multi-GB exports
are no longer bottlenecked on pointless re-compression.
- Report progress through the foreground notification (alert once, then
silent) and dedupe concurrent exports for the same app via unique work.
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