[FEATURE] Add a Visual Identifier for Foreign Key Columns

[lethalSopaper]

Description
It can be difficult to quickly identify foreign key (FK) columns. This is especially challenging when a foreign key's column name is different from the primary key it references in the parent table. This ambiguity requires developers to manually trace relationship lines or inspect table properties to confirm the connection, which can be inefficient and susceptible to errors.

Proposed Solution
To improve diagram readability and usability, introduce a distinct visual indicator for all foreign key columns. One effective solution would be to display the text of FK columns in a unique, consistent color. This would allow users to identify all foreign keys in a diagram at a glance, making the relationships between tables much clearer.

[lethalSopaper]

This is issued in #66.