### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### The Feature

Add a `spend` field to `POST /team/member_update` so a team member's accrued spend can be set through the API.

Today `LiteLLM_TeamMembership.spend` — where per-team-member spend is tracked (`LiteLLM_BudgetTable` has no `spend` column) — cannot be set through any management endpoint. `POST /team/member_update` returns `200` when a `spend` field is included but silently ignores it (the field is not part of `TeamMemberUpdateRequest`), and no other endpoint writes member spend.

The field should write both the membership row and the cross-pod spend counter that enforcement reads (`spend:team_member:{user_id}:{team_id}`), so the change is honored immediately — see the sibling bug #30776 for why a DB-only write to that counter is not enough.

### Motivation, pitch

`/key/update` and `/user/update` already expose `spend` as an updatable field, but team members have no equivalent. This makes it impossible to administratively correct or lower a member's accrued spend (apply a one-time credit, fix an over-count, undo a mischarge) — operations already possi…