### Check for existing issues

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

### The Feature

I would like LiteLLM to support a configurable reporting timezone for usage, spend logs, exports, and Admin UI display.

Suggested behavior:

1. Admins can configure a global reporting timezone. 2. Usage and spend date filters use the configured timezone for business-day boundaries. 3. CSV/export timestamps can be formatted in the configured timezone. 4. Admin UI displays usage/spend times consistently. 5. Optional future support for org/team/user-level timezone defaults.

Example:

```yaml general_settings: reporting_timezone: Asia/Shanghai

### Motivation, pitch

Many companies operate usage and finance reporting by a fixed business timezone rather than UTC or the browser timezone.

For example, a company may define monthly usage, daily reports, and billing exports using `Asia/Shanghai`. If backend aggregation uses UTC while UI or exports use local time, totals can appear inconsistent around day/month boundaries.

A configurable reporting timezone would make LiteLLM usage and spend reports easier to reconcile with internal business reporting. …