bug(sidenav): Sidenav opening animation triggers on page navigation

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

When using Angular Material’s Sidenav with `mode="side"` and `opened="true"`, navigating between pages triggers the opening animation, even though the sidenav is already in the open state. This behavior is inconsistent with the initial navigation, where the animation does not occur (which is the expected behavior).

### Reproduction

Steps to reproduce:
1. Go to https://material.angular.dev/components/sidenav/overview
2. Click on any link and go back to the previous page

### Expected Behavior

If the sidenav’s opened input is set to true initially, the opening animation should not play when moving between pages.

### Actual Behavior

The opening animation is triggered on page navigation, even if the sidenav is already open.

### Environment

- Angular: 21.2.6
- CDK/Material: 21.2.6
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

Comienza con la implementación de Angular Material Sidenav y reproduce el comportamiento de los pasos del issue en material.angular.dev usando mode="side" y opened="true". Rastrea qué ocurre durante la navegación entre páginas después de la carga inicial y, a continuación, verifica que la navegación ya no active la animación de apertura mientras el sidenav permanece abierto.

Escrito por el modelo de indexación a partir del texto del issue.