Encrypted storage

[kirillt]

We can add [encrypt] operation for a resource of any kind. Upon activation, the resource would be encrypted and moved into .ark/encrypted subfolder.

A password should be used for encryption and decryption, but it would be nice to use PIN-code for decryption (so we would store encryption keys and unlock them when PIN is valid). Fingerprint instead of PIN can be used as well (must be configurable).

The resource must be possible:

1. To share in encrypted form, e.g. send via a messenger.
2. To decrypt without the app.

To achieve these, some common algorithm and format must be used. See https://github.com/C2SP/C2SP/blob/main/age.md and https://github.com/str4d/rage.

Encryption would break last modified attribute, so first discovered or "our own" last modified should be used, see ARK-Builders/arklib#66 for the inspiration. It would be nice to sort resources in the way like they are without encryption, just asking PIN code for displaying protected resources.

[kirillt]

Encrypted resources should be labeled by special encrypted tag automatically.