feat(account): show go-to-market balance

[fatflowers]

Summary

• add the top-level go_to_market_balance_micros_usd field to the balance response type
• show GTM balance separately in the human-readable aisa balance output
• cover the account, API-key-available, and GTM balance values in account command tests

Validation

• npm test -- tests/account.test.ts
• npm run build
• git diff --check