Show 'Badge not available on Indie' near Notifications toggle and in docs

Description: As an Indie plan user, I want a clear indicator in the Admin UI (near the Notifications toggle) and an explicit note in the documentation that the notification badge counter is not available on the Indie tier, so I immediately understand the limitation and what to do next. Problem: Currently, the UI allows enabling Notifications and the docs do not explicitly state that the badge counter is unavailable on the Indie tier. This leads users to expect a badge that never appears, causing confusion, repeated troubleshooting, and unnecessary support escalations. Benefit: Sets accurate expectations for Indie users. Reduces support tickets and escalation. Provides clear upgrade guidance without trial-and-error. Improves transparency about plan-gated features.