"Later" button for initial roots indexing

When file system scan is complete and roots are discovered, the app begins indexing all discovered roots. This easily can be very long operation and we don't want to make user wait for 10 roots to index before they could open only 1 particular root. Capability to postpone total indexing should be implemented.


Start by tracing the flow from filesystem scan completion and root discovery into indexing, then inspect the screen shown in the attached image. Determine how a “Later” action can defer indexing all discovered roots while still allowing a selected root to open. Done means users can postpone total indexing and access one root without waiting for every root to finish.

Written by the indexing model from the issue text.