fix: avoid avatar update when opening profile

[almacbe]

Description

Fixes #5577

AvatarSettings treated its initial effect as a user change and persisted the current avatar whenever the profile opened. It now dispatches editSelf only when the local avatar is semantically different from the persisted avatar.

This keeps the intentional migration for older avatars without backgroundColor, because the completed avatar still differs from the stored value and is persisted once. Regression tests cover initial mounting, real and duplicate shuffle results, optimistic updates, legacy avatars, and missing avatars.

Changelog

• Skip avatar updates when the local and persisted avatar values are deeply equal.
• Keep optimistic persistence for real avatar changes and legacy avatar migration.
• Add behavioral coverage around the API.editUser boundary.

Checklist

• I have performed a self-review of my own code
• I have written and understand every part of this contribution myself - if AI tools were used, I have thoroughly reviewed and verified all changes
• I have commented my code, particularly in hard-to-understand areas
• The light- and dark-theme are both supported and tested
• The design was implemented and is responsive for all devices and screen sizes
• The application was tested in the most commonly used browsers (e.g. Chrome, Firefox, Safari)

(Optional) Visual Changes

None. This change does not alter the UI.

[Schwehn42]

is the duplicate toHaveBeenCalled check necessary?