update partners for CloudBrew 2026

[GlennColpaert]

This pull request updates the "Partners" section of the index.html file to reflect the current year's partners and revises the display of platinum and silver partners. The most important changes are:

Partner section updates:

• Changed the section heading from "Last year's partners" to "This year's partners" to reflect the current event sponsors.

Platinum partners list:

• Updated the list of platinum partners by removing several previous sponsors and leaving only Codit and Zure as platinum partners.

Silver partners list:

• Removed all previously listed silver partners, leaving the section effectively empty except for a placeholder column.