Allow Cards to reference or link to other items (Cards, Sticky Notes, Text blocks, or Boards)

Currently, in Noteey, Cards cannot contain internal references or links to other items — unlike Sticky Notes or Text blocks, which allow linking to another element within the same board or across different boards.
This limitation breaks consistency between item types and prevents Cards from being part of a fully interconnected “second brain” system.

As a user who relies on Noteey for structured thinking and organizing information, I need to be able to link a Card to another Card, Sticky Note, Text block, or even to a specific Board — both within the same board and across boards.