Refresh "Invested" header balance after investment completes

[Copilot]

The shell header's "Invested" balance stayed stale after a new investment because WalletsUpdated was only fired at the start of the payment flow (before the draft was built), never after the investment was saved to local storage.

Changes

• InvestPageViewModel.PayWithWalletAsync — fire RefreshBalanceAsync(walletId) after successful submission (both auto-approved and founder-approval paths)
• InvestPageViewModel.PayViaInvoiceAsync — same fix for the invoice payment path

_logger.LogInformation("Investment flow completed — advancing to Success screen");
_ = _walletContext.RefreshBalanceAsync(walletId);  // triggers WalletsUpdated → LoadTotalInvestedAsync
CurrentScreen = InvestScreen.Success;

RefreshBalanceAsync fires WalletsUpdated, which causes ShellViewModel.LoadTotalInvestedAsync to read the already-updated InvestmentRecordsDocument from local storage and display the correct invested total.