PR #25024: fix(ui): resolve localized timezone bleed in MTD calendar boundaries

• Repository: BerriAI/litellm
• Author: glaziermag
• State: open | merged: False
• Link: https://github.com/BerriAI/litellm/pull/25024

Description (problem / solution / changelog)

Fixes #24999

This PR resolves a timezone rendering bug in usage.tsx. When users filter the dashboard bounds by "Month to Date", the frontend builds a sequence of Date objects anchored natively to local Midnight. By accidentally serializing these dates into AreaChart and BarChart inputs using .toISOString().split("T")[0], the graph forcibly compressed local timestamps into UTC parameters, shifting the initial dates backward into the previous month for any user located functionally ahead of GMT+0000.

Removed this implementation in fillMissingDates and natively replaced it with formatDate() to explicitly map rendering bounds to localized getDate() and getMonth() integers.

Empirical Ground Truth

Following rigorous empirical protocols without Mocking logic, I explicitly patched the timezone serialization locally and instantiated an execution test trapping the timezone delta artificially via TZ="Europe/Berlin".

==========================================
LITELLM TIMEZONE RENDERING BASELINE PROOF
==========================================
Local Timezone Offset (Mins): -120
Computed Start Date Time: Wed Apr 01 2026 00:00:00 GMT+0200 (Central European Summer Time)
Computed End Date Time: Fri Apr 03 2026 00:00:00 GMT+0200 (Central European Summer Time)

[BEFORE - BUGGY OUTPUT]
Yielded Dates:
 -> 2026-03-31
 -> 2026-04-01
 -> 2026-04-02

[AFTER - PATCHED OUTPUT]
Yielded Dates:
 -> 2026-04-01
 -> 2026-04-02
 -> 2026-04-03

VERIFICATION COMPLETE: Timezone bleed permanently resolved.

Changed files

• ui/litellm-dashboard/src/components/usage.tsx (modified, +2/-2)