Release v9 bytes no row owns, and reuse the v9 blob on a replace

[dmurphy5]

Description

Two fixes for apps that upgrade from v9 with a chunked upload still pending. Diana's v10 cutover resumes those uploads with a same-id mutate() over the v9 manifest, so both paths matter at release.

• cancel(id) on an id with no row now deletes the id's directory when it has no entry file. A v9 chunked upload that was still running at the upgrade gets no legacy row, so before this its manifest and blob could never be released.
• A same-id mutate() over a legacy row whose v9 manifest could not be read now runs over the v9 blob. Before, it ignored the blob and failed with E_FILE_MISSING once the caller's source was gone. A caller file that exists still takes priority. Fixed on Android and iOS.

What to look at

• QueueStore.removeUnowned on both platforms: what counts as unowned, and that it runs under the store lock on Android and on the coordinator's queue on iOS.
• The legacy fallback in Android QueueController.decideAndCommit and iOS QueueCoordinator+Enqueue.swift.

Decisions and trade-offs

• The rule is "no entry file", not "only v9 files". It also removes a body a failed enqueue staged and left behind, which nothing else would delete.
• A failed delete is not reported, and cancel() still resolves. Release is best effort, like the rest of the v9 cleanup.
• cancel("") does nothing, as before.

Test plan

• yarn lint:ci, yarn typecheck, yarn test (189 tests): pass.
• Android unit tests (:react-native-background-upload:testDebugUnitTest, 313 tests): pass. New cases cover cancel of a row-less v9 folder, of an id with no folder, and a replace over a legacy row with a corrupt manifest.
• swift test in ios/ (210 tests): pass. New cases cover the iOS cancel and the unreadable-manifest replace. Each new case fails with its fix removed.
• Not run on a device.

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