Get the workspace's current Nurama Credit balance.

Returns the workspace's spendable Nurama Credit balance. Requires `canGetCreditBalance` on the workspace (workspace owner / admin, project owner / admin) and an active subscription; no per-feature gate. The balance is also returned as `balanceAfter` on every billable AI call, so clients can keep a balance display fresh without a separate fetch after every call. `balance` is the spendable total: `planBalance` (monthly plan grant, does not carry over) + `purchasedBalance` (top-ups, accumulates). `hasPriorTopUp` reports whether the workspace has ever made a manual credit purchase — the precondition for enabling auto top-up. Also available at `GET /credits/balance` (same response).

curl -X GET "https://example.com/ai/balance?workspaceId=497f6eca-6276-4993-bfeb-53cbbbba6f08"

{  "balance": 9997,  "planBalance": 5000,  "purchasedBalance": 4997,  "hasPriorTopUp": true}