Update sponsor page: reorganize sponsors and add BNP Paribas Group

- Reorganize sponsors into tiers: Founding (Inria), Gold (Chanel), Silver (BNP Paribas Group), Bronze (NVIDIA)
- Remove logos from Past Sponsors section, convert to full-width text format
- Convert Other contributions section to bullet points
- Add BNP Paribas Group logo and update sponsor information
- Add AXA, BNP Cardif, and Dataiku to past consortium sponsors grid
- Update probabl description to mention sponsorship program management
- Update footer funding logos
- Simplify sponsor descriptions for consistency

Author: fanfcorp