fix(android): preserve account-owned background uploads

[veryCrunchy]

What changed

• resolve queued Deck attachment uploads through their persisted account owner instead of the active account
• load that account's credential without changing account selection
• fail closed when the account is removed or the loaded credential does not match the persisted owner
• retain the existing encrypted account-scoped queue and upload ambiguity handling

Why

A queued upload for account A was permanently marked failed and its persisted URI capability was released when account B became active. The durable store already recorded A as the owner, but the worker ignored it when choosing credentials.

Validation

On the dedicated Linux build host, from exact parent #436 head cd2b6de4156e42c9be02840d264790dc5c23a4e4:

• focused AndroidDurableMultipartUploadPolicyTest
• :androidApp:assembleDebug
• bash tools/check-kotlin-architecture.sh
• bash tools/check-repository.sh, repeated after binding PR fix(android): preserve account-owned background uploads #438 in the changelog fragment

Limits

• deterministic tests cover same-server accounts, exact credential selection, missing-owner refusal, and credential mismatch refusal
• the existing Android instrumented durable-store test covers two accounts with the same remote upload path, but this pass did not start an emulator or repeat that unchanged test
• no live Nextcloud upload was performed

Found by the code-first account-isolation audit. Depends on #436.

[obiente-cloud]

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[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-01T21:58:56.323238Z	5fee12e	New commits

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