[Bug] Trading widget: unformatted balance and est. cost values

[realproject7]

Problem

The trading widget shows raw 18-decimal values without formatting:

• Balance: 5034.425044895956140455 HUNT — should be 5,034.43 HUNT
• Est. cost: 68.623631443223832041 HUNT — should be 68.62 HUNT

Fix

Format balance and est. cost displays to a reasonable precision:

• Values >= 1: 2 decimal places (e.g. 5,034.43)
• Values < 1 but >= 0.001: 4 decimal places (e.g. 0.0033)
• Values < 0.001: 6 decimal places or scientific notation
• Add thousands separators for large numbers

Apply to all pay token modes (ETH, USDC, HUNT, PLOT).

File

src/components/TradingWidget.tsx — balance display and est. cost display

Branch

task/789-trading-format