Instead of showing all 4 billing providers as separate full-width cards,
the billing section now shows:
- When no billing connected: a compact 4-column grid picker to select
your billing platform (Gaiia, Sonar, Splynx, VISP)
- When one is active: a single card showing the connected provider with
status, sync info, and a note to disable before switching
This reduces visual clutter since users only ever use one billing system.
Non-exclusive categories (QoE, Incidents, Infrastructure) remain as
individual cards since multiple can be active simultaneously.