[Feature Request] Simplified navigation entries for common document categories

Description Problem The current navigation and filtering system in Paperless-NGX is already very powerful, especially for administrative users. After some onboarding, configuration elements and saved views can be managed quite efficiently. However, in customer environments with less technical users, document filtering and view creation are still perceived as too complex. Users often struggle with: understanding filter composition, creating saved views, and managing shared navigation structures. The new shared saved views in v3.0.0 beta are a great step in the right direction, but they still require manual setup and administration for every installation. Proposal Introduce a simpler way to expose frequently used document categories directly in the sidebar/navigation. Possible approaches: Option 1: "Show in navigation" toggle Allow entities such as: Tags Document types Correspondents to be marked with a simple option like: "Show in…