Enhance Campus Connect and Student Clubs base themes

[debciriaoc]

Hello team!

This update replaces the base themes for Campus Connect and Student Clubs (related to #1646).

Proposed changes:

• Replacement of the old campus-connect and student-clubs theme folders with updated versions.
• Cleanup and improvements to the README theme files for better documentation.

Key improvements:

• Enhanced responsiveness (better layouts on mobile and tablet devices).
• Replaced placeholder images with public domain / CC0-licensed ones (no copyright concerns).
• Added more templates: adjustments to index.php and creation of a custom 404.php template.

I've prepared everything in a branch on my fork: debiriac/wordcamp.org (branch: debiriacoc-update-wpcc-student-clubs).

Is it okay to proceed with a Pull Request using this approach (full folder replacement)?
I'm happy to make any adjustments