fix: default image in workspaces for image types

[abp6318]

1. Description:
   I realized there was a much nicer way to do this vs what I thought was needed previously. All we need to do is pass in a default thumbnail image string if the item is of type Image. The arcgis-hub-image-picker does all the work that I thought we'd need to add around the default image

2. Instructions for testing: see https://github.com/ArcGIS/opendata-ui/pull/15367

3. Closes Issues: https://devtopia.esri.com/dc/hub/issues/14191

4. Updated meaningful TSDoc to methods including Parameters and Returns, see Documentation Guide

5. Either ran npm run changeset or this change does not require a release.

6. These changes have been verified by QA using a ?uiVersion that includes a PR-Preview of this branch and the v_req label has been applied to the issue.

7. OD-UI E2E tests pass against these changes using a ?uiVersion that includes a PR-Preview of this branch

[changeset-bot]

🦋 Changeset detected

Latest commit: 1e2e10b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@esri/hub-common	Patch

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[Copilot]

Pull Request Overview

This PR fixes the default thumbnail image display for Image-type items in workspaces by passing the item's data URL as the default thumbnail. The solution leverages the existing arcgis-hub-image-picker component rather than adding new custom logic.

Key Changes:

• Added getDefaultImageEntityThumbnail helper function to determine if content is an Image type and return its data URL
• Modified getThumbnailUiSchemaElement to accept an optional defaultThumbnailUrl parameter
• Updated buildUiSchema in ContentUiSchemaEdit to pass the Image entity's data URL as the default thumbnail

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

File	Description
packages/common/src/core/schemas/internal/getThumbnailUiSchemaElement.ts	Added getDefaultImageEntityThumbnail helper and updated function signature to accept optional default thumbnail URL
packages/common/src/content/_internal/ContentUiSchemaEdit.ts	Updated thumbnail UI schema call to include default image for Image-type content
packages/common/test/core/schemas/internal/getThumbnailUiSchemaElement.spec.ts	Added tests for new getDefaultImageEntityThumbnail function
.changeset/giant-poets-fall.md	Added changeset documenting the fix

[knbhagat]

LGTM - Great job Aaron