doesn't save nzMode="week" when use step buttons

[maxonbigbon]

Reproduction link

https://stackblitz.com/run?file=src%2Fapp%2Fapp.ts

Steps to reproduce

you open the date selection in week mode, you need to move to the next month or year through the header. After clicking, the weeks backlight does not work as for week mode.

What is expected?

week mode must work properly, week light shows on each of months

What is actually happening?

week mode changes on date mode, so you don't see week light

Environment	Info
ng-zorro-antd	21.0.0
Browser	Yandex / Chrome / Firefox / Safari

[Laffery]

the reproduction link is invalid

[HyperLife1119]

This issue can indeed be reproduced in the official documentation. After switching months, the weekday highlight disappears.

The root cause is that after switching panels, the panelMode is reset from the original week mode to the date mode.