Returns:
  - balance: subscription credits remaining (resets weekly to weekly_allocation, capped at max_balance)
  - prepaid_balance: pre-paid credits remaining (no expiration; consumed after sub balance is empty)
  - total_available: balance + prepaid_balance (the actual amount you can spend right now)
  - weekly_allocation: sub credits added every 7 days
  - max_balance: rollover ceiling for sub credits (4× weekly_allocation)
  - tier: free / pro / unlimited / enterprise
  - max_concurrent_calls: parallel call limit for your tier
  - next_reset_at: ISO timestamp when next weekly grant happens
  - pricing_version: currently active pricing version
  - prepaid_packs: list of available credit-pack sizes + EUR prices for your tier

This tool is FREE in all tiers — never costs credits to check your balance.