phase 8: UI/UX overhaul — layout, charts, map, data freshness
- Fix ticker tape CLS with skeleton loader and fixed height
- Add Inter font, max-width container, responsive dvh units
- Hero metrics: trend deltas, per-metric sparkline colors, 3+2 grid
- GPU calculator: step=100 slider + text input, PUE factor, region comparison bars
- Grid stress: replace misleading arc gauges with demand status bars
- Demand summary: expand to 4-metric highlights grid
- Charts: responsive heights, ISO/non-ISO toggle, correlation R² + trend line
- Map: US-wide default view, marker clustering, enriched region panels, zoom controls
- Fix NYISO polygon (NYC), MISO polygon (Michigan), MISO south (MS/LA)
- Add automated ingestion via instrumentation.ts
- Add data freshness indicator in footer
- Fix backfill start date to 2019-01-01 (EIA RTO data availability)
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