Defaults to localhost:3000 for local dev. Server deployments can
pass a comma-separated list via the environment.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
New GET /history endpoint fetches 365 days of BTC/EUR data from
CoinGecko, deduplicates by date, and joins the user's purchases.
BTCHistoryChart component renders the price line with orange dot
markers on purchase dates and a dashed cyan avg buy price line.
Tooltip shows purchase details on marked dates.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>