[Research] Price chart: feasibility of USD-based chart

[realproject7]

Question

The price chart currently shows price in PLOT tokens (from `trade_history.price_per_token`). Is it feasible to display it in USD instead?

Known constraints

• `trade_history` stores `price_per_token` in PLOT, not USD
• We do NOT store the PLOT→USD exchange rate at the time of each trade
• Converting historical PLOT prices to USD retroactively would require historical PLOT/USD price data we may not have

Task

1. Investigate whether we have (or can get) historical PLOT→USD prices for each trade timestamp
2. If yes: convert the chart to USD. Multiply each `price_per_token` by the PLOT/USD rate at that timestamp
3. If no: keep the chart in PLOT but add a note/tooltip showing the current USD equivalent of the latest price. Document why USD conversion isn't possible for historical data.
4. Report findings before implementing — don't guess

File

`src/components/PriceChart.tsx`, `trade_history` table schema

Branch

`task/776-chart-usd-research`