[Bug] DonateWidget: unformatted balance shows raw 18-decimal values

[realproject7]

Problem

DonateWidget.tsx displays raw 18-decimal balance values (e.g. 5034.425044895956140455) — same bug that was fixed in TradingWidget via PR #791.

Solution

Apply the same formatTokenAmount helper from TradingWidget (or extract to shared src/lib/format.ts) to the balance display in DonateWidget (lines ~152, 164).

Acceptance Criteria

• Balance values formatted to 2-4 decimal places with thousands separators
• Reuse or share the formatting logic from TradingWidget

Branch

task/<issue>-donate-format