Calendar week starts on Tuesday instead of Monday

[kppethe]

Checklist

• I have enabled debug logging for my installation.
• I have filled out the issue template to the best of my ability.
• This issue only contains 1 issue (if you have multiple issues, open one issue for each issue).
• This issue is not a duplicate issue of any previous issues..

Describe the issue

The built-in Maint sidebar panel calendar displays the week starting on Tuesday instead of Monday, causing all dates to appear in the wrong column. See screenshot below:

The calendar week starts on Tuesday. All dates are shifted one column to the right — for example, Monday 9 March 2026 appears in the Tuesday column.

Notes:
The native Home Assistant calendar view displays dates correctly with Monday as the first day of the week or Sunday if so chosen in the settings, so this appears to be specific to Maint's custom frontend calendar component.

Reproduction steps

1. Go to 'Maintenance' from sidebar
2. Click 'Create Task'
3. Click Calendar Icon

Debug logs

[Masterz69]

Confirm, wekkdays shifted for one:

2026 June 26 is a Friday, but shown as Saturday.