# Date Navigation Feature - Walkthrough

We have implemented a Date Navigation feature for the Health Dashboard, allowing you to explore historical health data.

## Features Added

1.  **Date Navigator UI**:
    *   Added `Previous` (<) and `Next` (>) arrow buttons.
    *   Added a central Date Display text (e.g., "Today", "Dec 21", "Dec 20 - Dec 26").
    *   Responsive design: Visible on both mobile and desktop.
    *   Styled with TailwindCSS for a clean, professional look consistent with the existing theme.

2.  **Navigation Logic**:
    *   **Day View**: Moves back/forward by 1 day.
    *   **Week View**: Moves back/forward by 7 days.
    *   **Month View**: Moves back/forward by 1 month.
    *   The Date Display updates dynamically to reflect the current period.

3.  **Backend Updates**:
    *   Updated `/api/health/stats` endpoint to accept a `ref_date` parameter.
    *   Modified database queries to filtering data `between(start, end)` based on the selected reference date.
    *   This ensures you can view past weeks and months accurately.

4.  **UX Improvements**:
    *   **Empty State Handling**: If you navigate to a date with no data, the dashboard fields reset to `--` placeholders instead of showing stale data from the previous view.
    *   **Loading Feedback**: Existing toast notifications indicate if data loading fails.

## How to Verification

1.  Open the Health Dashboard.
2.  You should see the new Date Navigator explicitly to the left of the "Day/Week/Month" toggle.
3.  Click `<` to go back in time. The data (steps, sleep, heart rate, etc.) should update.
4.  Switch to "Week" view. The date text should show a range (e.g., "Dec 15 - Dec 21").
5.  Click `>` to return to recent dates. "Today" will be displayed when you are back to the current date.