[feature/ux improvment] Allow using shared files in eSigner and show files from signing invite in File Manager shared list

[krivtsova-arina]

Description

Currently:

1. Files shared with a user in File Manager aren't available for selection in eSigner when creating a signing container.
2. Files from invites for sign don't appear in File Manager shared list

My opinion, this behavior is confusing from a UX perspective and breaks the mental model of “one document — one lifecycle across services”.

Acceptance Criteria

1. Files shared with a user in File Manager should be selectable in eSigner for signing.
2. Files from invites for sign should appear in File Manager in Shared section