feat(pdf): add optional tile borders to PDF export (#1954)

[dhruv-git-sys]

Add optional tile borders to PDF export (#1954)

This PR adds an option to show borders around tiles when exporting boards as PDF.

• Adds a checkbox in the Export UI for "Show borders around tiles in PDF".
• Passes the option through the export container and helpers.
• Updates the PDF export code to draw a border around each tile if selected.
• Updates the changelog.

Fixes #1954

Screenshots (if applicable): (Add screenshot of the new checkbox if you have one)

[RodriSanchez1]

This is awesome! I will do the review this week. Thanks a lot