Replace 260×60 sparkline with full 520×200 SVG line chart:
- Multi-vendor colored polylines (up to 8, MAGATAMA indigo palette)
- USD-normalized prices (EUR×1.08, GBP×1.27)
- Y/X axes with grid lines, date labels, price labels
- Hover vertical cursor + floating tooltip per-day vendor prices
- Click-to-toggle vendor legend
- 7d / 14d / 30d time range selector with live API re-fetch
- Current best prices table below the chart
- End-point dots per vendor line
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