dashboard: restore SA-style main layout with icon status rows and gauges

- Main Dashboard now has the requested SolarAssistant-style layout:
  left column with icon status rows (Inverter, Solar PV, Grid, Battery)
  plus gauges (Load, Solar, Grid, Battery), right column with charts
  (PV Today, 24h Overview, Battery Power, Battery SOC).
- Clicking any status row or gauge drills into the subsystem detail view.
- Keep top tabs: Main, Charts, Historical, Automation, Configuration.
- Charts tab: 30-day per-subsystem bar charts.
- Historical tab: 1-year charts plus daily totals.
- Automation and Configuration tabs unchanged from previous commit.

Author: Jeremy Ewing