Protect connections and define device-backup boundaries #94

Parent

#91

What to build

Move each local account connection into UUID-keyed iOS Keychain or Android Keystore-backed storage, while keeping committed saved data eligible for normal device backup and excluding temporary Cyd Bluesky archive material.

Acceptance criteria

• Legacy OAuth material is removed from AsyncStorage only after the protected write succeeds, and migration is safe to resume after termination.
• Connections are isolated by local-account UUID and are absent from runtime databases and Cyd Bluesky archives.
• Disconnecting removes the connection while retaining the local account and its saved data; deleting an account removes both.
• Committed per-account databases and media remain eligible for OS-managed device backup.
• Import/export staging and reproducible caches are excluded from device backup.

Blocked by

• None — can start immediately.

(This was written by an LLM.)