Handling duplicates in Aggregated mode

In aggregated mode, the resources grid displays resources with the same content coming from different roots. Duplicates must be filtered out, one id — one item in the grid. Number of duplicates should be presented to the user though and all data related to duplicated resource should be written in all roots it comes from.

E.g. we have a resource `12-345345` stored in folders `/home/user/A` and `/home/user/B`.
User puts tag `test` on it. The app must write this record both into `/home/user/A/.ark/tags` and `/home/user/B/.ark/tags`.

UI should present the information about duplicates in the details dialog.

Start by locating the aggregated-mode resource grid, the details dialog, and the code that writes tag data to each root. Trace how identical resources are identified and how tags are persisted across roots. Done means the grid shows one item per resource with a duplicate count, the details dialog exposes duplicate information, and updates are written to every source root.

Written by the indexing model from the issue text.