I've changed quite some things here. Attempt of a summary:

* storageKey is now only controlled by useVaultStorageState

I've noticed that dealing with how storage keys are generated (to apply user scope) was handled in two places: the existing wallet code and in the new vault code.

This was confusing and error-prone. I've fixed that by completely relying on the new vault code to generate correct storage keys.

* refactored migration

Migration now simply encrypts any existing local wallets and sends them to the server. On success, the local unencrypted version is deleted.

The previous code seemed to unnecessarily generate new local entries prefixed by 'vault:'.

However, since we either use unencrypted local state OR use the encrypted vault on the server for the data, I didn't see any need for these.

Migration seems to work just as well as before.

* removed unnecessary state

In the <DeviceSync> component, enabled & connected were using a unnecessary combo of useState+useEffect.

They were only using variables that are always available during render so simple assignments were enough.

* other minor changes include:

  * early returns
  * remove unnecessary SSR checks in useEffect or useCallback
  * formatting, comments
  * remove unnecessary me? to expose possible bugs

This didn't cause any bugs because useWallet returns everything we need on first render.

This caused a bug with E2EE device sync branch though since there the wallet is loaded async.

This meant that during payment, the wallet config was undefined.

This adds 'perDevice' as a new wallet field to force local storage. For example, WebLN should not be synced across devices.

…buttons for testing

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