Update 10: Portfolio chart

The dashboard now has a Portfolio value chart: what you hold through Plynth, day by day, over the last week, month or
three months. It adds up your USDG and your Stock Tokens, with each day's Stock Token value taken from that day's
Chainlink price on Robinhood Chain, and shows how much the total moved over the range you picked. Everything comes
from on-chain data Plynth already indexes; there is no outside market data.

Commit: 33db9d5
Full notes: CHANGELOG.md