Fix <SaveButton> form dirty status check

[djhi]

Problem

In react-hook-form versions greater than 7.53.0 (only tested 7.53.2), fields that are not dirty are still present in the dirtyFields state but with a false value. However, our current dirty check in <SaveButton> only check whether the dirtyFields state has object keys.

Solution

Actually check whether any of the dirtyFields state keys have a true value to determine the dirty status.

How To Test

• https://react-admin-storybook-git-fix-save-button-dirty-check-marmelab.vercel.app/?path=/story/ra-ui-materialui-button-savebutton--complex-form
• Modify any input and check the <SaveButton> disabled state after/before saving.

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.

[Copilot]

Pull Request Overview

Fix SaveButton dirty state detection to align with react-hook-form ≥ 7.53.x where dirtyFields includes keys with false values.

• Replace naive key-length check with a recursive hasDirtyFields function.
• Add a ComplexForm Storybook story and a corresponding test to validate behavior with nested/array fields.

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
packages/ra-ui-materialui/src/button/SaveButton.tsx	Introduces hasDirtyFields to properly compute isDirty from dirtyFields, and uses lodash isEmpty for array-item handling.
packages/ra-ui-materialui/src/button/SaveButton.stories.tsx	Adds ComplexForm story to reproduce and visualize dirty state in complex forms (arrays of objects).
packages/ra-ui-materialui/src/button/SaveButton.spec.tsx	Adds a test to ensure SaveButton enables/disables correctly with nested/array fields and updates a test title for clarity.

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