feat(fileinput): implement controlled file input with onChange callback

[stdavis]

This is to support clearing the FileInput state in WRI advanced search.

[Copilot]

Pull request overview

This PR implements controlled component support for the FileInput component, enabling external state management and programmatic clearing of files. This is needed to support clearing the FileInput state in WRI advanced search.

Key changes:

• Replaced onSelect callback (receiving FileList | null) with onChange callback (receiving File[] | null)
• Added value and onChange props to support controlled mode while maintaining backward compatibility with uncontrolled mode
• Simplified file management by removing DataTransfer API complexity
• Updated ReactHookForm integration to use the new controlled API

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
packages/utah-design-system/src/components/FileInput.tsx	Implements controlled/uncontrolled component pattern with value/onChange props, replaces onSelect with onChange callback, simplifies file state management
packages/utah-design-system/src/components/FileInput.stories.tsx	Updates ReactHookForm story to use new onChange API, adds Controlled story demonstrating external state management with reset functionality

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[github-actions]

Visit the preview URL for this PR (updated for commit 1451cc4):
Firebase Preview: https://ut-dts-agrc-kitchen-sink-dev--feat-controlled-file-inp-neuf0vvr.web.app
_{(expires "2025-12-19T18:57:43.787312910Z" )}

[Copilot]

@stdavis I've opened a new pull request, #569, to work on those changes. Once the pull request is ready, I'll request review from you.