feat: set default date as image date on ChangeDateAction

[RenautMestdagh]

Description

When selecting multiple images and changing their date. Currently the default date when the dialog opens is today's date.

Setting the default to the datetime of 1 of the selected image(s) is vastly more relevant than using today's date, especially when editing historic assets. This change eliminates the significant hassle of forcing users to manually scroll back and select a specific past date (like one from 2005) just to make a quick time adjustment, while still leaving the current date easily accessible via the date picker.

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

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[danieldietzler]

Please fix the failing tests