Plan: Fix Timezone Handling in Wakeup Times Module

Problem Description

The "Wakeup Times" chart (in frontend/src/components/stats/WakeupPlot.tsx) displays wakeup times incorrectly due to a timezone mismatch.

Observation: If a baby wakes up at 05:55 local time (e.g., in UTC+2), the chart shows 03:55.
Cause: The backend stores times in UTC. The frontend currently receives minutes relative to UTC midnight and renders them directly using formatMinutesAfter without applying the client's local timezone offset.

Backend Verification:
- Examine backend/app/routers/stats.py (or equivalent) and the CRUD logic to confirm that wakeup_minutes is calculated based on UTC midnight.
- Verify how the backend handles the wakeup_ref and bedtime_ref parameters.
Frontend Logic Audit:
- Trace the data flow from fetchWakeSleepTimes -> useStats -> WakeupPlot.tsx.
- Confirm that wakeup_minutes is indeed a raw offset from UTC midnight.

Calculate Local Offset: Use new Date().getTimezoneOffset() in the frontend to determine the difference between UTC and local time.
Adjust Minutes:
- In WakeupPlot.tsx, modify the mapping logic to adjust day.wakeup_minutes by the local timezone offset before it is passed to formatMinutesAfter.
- Formula: local_minutes = utc_minutes - (timezone_offset_in_minutes). (Note: getTimezoneOffset() returns minutes positive for west of UTC, negative for east, so subtraction is correct to add offset to UTC).
Refactor Utilities (if needed): If the logic is used elsewhere, consider moving timezone-aware formatting to frontend/src/utils/time.ts.

Manual Verification:
- Mock a response from the backend with a known UTC time.
- Check if the rendered string matches the expected local time.
Automated Testing:
- Add/update a test case in frontend/tests/e2e/stats.spec.ts (or a unit test in frontend/tests/) that simulates different timezone offsets to ensure the display is correct.
Regression Check:
- Ensure BedtimePlot.tsx and other time-related components are not negatively impacted by changes to shared utilities.