Fix #270: Add CAL Coding Guidelines PDF and fix broken link

[JeremyVyska]

Description

Fixes #270

The download link for the CAL Coding Guidelines PDF was broken (pointing to an external blog post that no longer hosts the file). This PR resolves the issue by:

1. Adding the PDF file to the repository in static/files/
2. Updating the markdown link to point to the locally hosted PDF

Changes

• Added static/files/CAL-Coding-Guidelines-at-Microsoft-Development-Center-Copenhagen.pdf
• Updated link reference in content/docs/NAVPatterns/3-cal-coding-guidelines/_index.md from external URL to /files/CAL-Coding-Guidelines-at-Microsoft-Development-Center-Copenhagen.pdf

Benefits

• ✅ Link is now stable and won't break again
• ✅ PDF is version-controlled alongside the documentation
• ✅ Works offline and in local builds
• ✅ Self-contained repository

Testing

• Verified the PDF download link works on the live site
• Confirmed PDF content is correct and readable