feat: add featured image caption block

[chickenn00dle]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Closes https://linear.app/a8c/issue/NPPD-1187/captioncredit-block-for-featured-images

This PR adds a featured image caption block to the block theme and adds the block to every template which contains a featured image.

How to test the changes in this Pull Request:

1. Go to any post and add a featured image or featured image block to the post.
2. Add the featured image caption block to the page
3. Save and view the post on the frontend. Confirm the featured image caption appears as expected
4. Back in the editor select the featured image caption block and add custom text
5. Save. View the featured image meta by selecting 'Replace' and confirm the caption did not change.
6. View the post on the frontend. Confirm the featured image caption appears as expected
7. Go back to the editor and remove the featured image.
8. Confirm the featured image caption block displays placeholder text asking you to add a featured image.
9. Save and view the post on the frontend. Confirm the featured image caption block is not present.
10. In the editor, add the query loop block and add the featured image and featured image caption blocks and save.
11. Verify the query loop displays the featured image captions correctly in the frontend
12. Via the site editor, go to any post template and confirm the featured image caption block is present.
13. Make changes and save. Verify the changes reflect correctly on the front-end

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[Copilot]

Pull request overview

This PR adds a new custom block for displaying featured image captions with optional media credit information. The block integrates with the Newspack Image Credits plugin to automatically display caption and credit metadata, while also allowing users to override with custom caption text.

Changes:

• Added a new newspack-block-theme/featured-image-caption block with editor UI and server-side rendering
• Integrated the block into all post and archive templates that display featured images
• Implemented support for automatic caption/credit display from media metadata with custom override capability

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
includes/blocks/featured-image-caption/class-featured-image-caption.php	PHP class for block registration and server-side rendering
includes/blocks/featured-image-caption/block.json	Block metadata and configuration
includes/blocks/featured-image-caption/edit.js	React component for block editor UI
includes/blocks/featured-image-caption/editor.js	Block registration entry point
includes/blocks/featured-image-caption/style.scss	Styles for placeholder text in editor
includes/blocks/index.php	Added require statement to load new block class
src/scss/blocks/_blocks.scss	Added import for block styles
templates/single/*.html	Added featured-image-caption block to all single post templates
templates/archive.html	Added featured-image-caption block to archive template
templates/author.html	Added featured-image-caption block to author template
templates/home.html	Added featured-image-caption block to home template
templates/search.html	Added featured-image-caption block to search template

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