Stats: Chart tooltip displays raw PHP date format string "F j, 2026" instead of parsed date

### Impacted plugin

Jetpack, Stats

### Quick summary

Jetpack Stats chart tooltip displays raw PHP date format string "F j, 2026" instead of the parsed date.
**Actual:** The tooltip text displays the literal string F j, 2026.
**Expected:** The tooltip text displays the correctly rendered date format (e.g., "Aug 23, 2026").

### Steps to reproduce

1. Log in to WordPress.com and open your site's dashboard.
2. Select the **Days** or **Week** view tab on the chart.
3. Hover over the bar representing August 23, 2026 (the third bar in the 7-day view).
4. Observe the tooltip header text.

### Image

### Site owner impact

Fewer than 20% of the total website/platform users

### Severity

Minor

### What other impact(s) does this issue have?

No revenue impact

### If a workaround is available, please outline it here.

_No response_

### Platform (Simple and/or Atomic)

Simple, Atomic

Start by reproducing the issue in the Jetpack Stats chart using the Days or Week view and hovering the August 23, 2026 bar. Search the repository for the Stats chart tooltip and its date-formatting logic, then verify that the tooltip renders a formatted date such as “Aug 23, 2026” rather than the literal format string.

Written by the indexing model from the issue text.