[Feature Request] Add a Last modified column to document lists and saved views

Description Current behavior In the document list, the display-field selector offers Added (added), but no Modified / Last modified (modified) field. This also prevents displaying the modification timestamp as a column in saved views. Sorting by Modified is already available, but the timestamps themselves cannot be compared directly in the list. Requested behavior • Offer an optional Last modified field alongside Created and Added. • Display the existing document modified timestamp as a column in table/list mode, using the usual localized date/time formatting. • Persist the selected column in saved views. • Ideally allow sorting ascending/descending by clicking the column header, using the existing Modified sorting. Use case When reviewing recently edited documents, I would like to see when each document was last changed without opening every document individually. Added only shows when a document entered Paperless and does not answer that question…