feat: interactive chart zoom — select a date range to inspect in detail

## Problem

The price history chart shows a fixed 90-day or 48-hour window. Users cannot zoom into a specific period to examine short-term price movements in detail.

## Requested behaviour

- Click and drag on the chart to select a date range
- Chart re-renders zoomed into the selected range
- Reset button or double-click to return to full range
- Works on both 90d and 48h views

## Acceptance criteria

- [ ] Drag-to-select on SVG chart
- [ ] Chart re-renders with selected range on x-axis
- [ ] Y-axis rescales to the zoomed data
- [ ] Reset zoom control visible when zoomed in