Monthly budgets and routing markup per LLM group

Each LLM group can now carry a monthly budget ceiling. When a group exceeds its budget, further requests are blocked with HTTP 402 until the next cycle, or until an administrator lifts the cap. Separately, operators can set a routing markup per group: Gateway tracks both the provider cost and the billed cost per request, so it is practical to resell capacity with transparent margin to downstream tenants and reconcile the difference in reporting. Both fields are editable from the admin groups page.

No action required. Budgets default to unlimited and markup defaults to zero.