Add PLOT balance to wallet card on profile page

[realproject7]

Requirement (Image 208)

The wallet card on the profile page currently shows just the address + copy button. Add the user's PLOT token balance with USD value.

Display

```
WALLET
0x4d68 ... b6c8 copy
Balance: 111,841.40 PLOT (≈ $1,901.30)
```

• Fetch PLOT balance via `erc20Abi.balanceOf(address)` using the PLOT token address
• Format with locale separators
• Show USD value using existing `usePlotUsdPrice()` hook
• Same font size and styling as other trust dashboard cards (Farcaster, X/Twitter)
• Works for any profile (public data), not just own profile

Files to modify

• `src/app/profile/[address]/page.tsx` — wallet card section

Branch

`task/693-wallet-plot-balance`

Self-Verification (T3)

• Wallet card shows PLOT balance with formatted number
• USD value displayed next to balance
• Styling matches other trust dashboard cards
• Works on other users' profiles (not just own)
• `npm run build` passes