Replace carousel item backgrounds with relevant image for portfolio item

[Copilot]

• Inspect current carousel implementation and existing validations
• Run baseline frontend/backend tests/build to capture pre-change state
• Implement minimal carousel background mapping from portfolio item data to relevant snapshots
• Update/add focused frontend tests for the new background behavior
• Run targeted frontend tests/build and capture a UI screenshot of the carousel
• Run final automated validation and summarize results

[Copilot]

Pull request overview

This PR updates the frontend portfolio carousel to display a more relevant background image per portfolio item by deriving the <img src> from either a provided image URL, a GitHub OpenGraph snapshot for GitHub repos, or a local color-based fallback.

Changes:

• Added helper logic in ControlledCarousel to choose between direct img URLs, GitHub OpenGraph snapshot URLs, and local fallback images.
• Updated the carousel rendering to use the new image-selection logic.
• Extended ControlledCarousel tests to validate GitHub snapshot image selection and fallback behavior for non-GitHub links.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
frontend/src/components/ControlledCarousel.js	Adds URL validation + GitHub OpenGraph mapping and uses it for carousel item images.
frontend/src/components/tests/ControlledCarousel.test.js	Adds a non-GitHub item and a test asserting GitHub snapshot vs fallback image behavior.

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