Goal for this part
Show the catalog in a ttk.Treeview with title, author, owned copies, and available copies.
Concepts: Treeview as a table
Treeview is Tkinter’s standard tabular widget. Each book id becomes a row iid so later parts can edit or borrow the selected row. Available copies equal owned copies minus open loans.
How to run it and what you should see
You should see seeded titles. Kindred should show fewer available copies than owned because of the seed overdue loan.