Transform the dashboard into a single-pane-of-glass command center that
blends operational metrics with business context from Gaiia subscriber data.
- Extend insight schema with multi-source support (snmp, gaiia, system)
- Add Oban workers for automated insight generation (device health, system, gaiia)
- New Dashboard context with health score computation and site summaries
- Rewrite dashboard LiveView with health overview, alert/insight feeds, site grid
- Add source filter pills for insights with URL state management
- Add metrics bar to site detail pages (device count, alerts, subscribers, MRR)
- Add subscriber/MRR context to alert list site links
- Add subscriber badges to device list site headers
- Real-time PubSub updates for alerts on dashboard