Puzzles/add hub blueprint layout provider

[gustavo-olmedo]

What is the value of this and can you measure success?

Provides a validated, maintainable blueprint for the new puzzles hub and a provider abstraction for future controllers.

Success is measured by contract and provider tests covering serialization, nested containers, archive entries, invalid JSON, resource loading, and stream closure.

What does this change?

• Adds the production puzzles-layout.json blueprint.
• Adds Scala models and Play JSON formats for the DCR payload.
• Adds an asynchronous PuzzlesLayoutProvider.
• Loads and validates the blueprint from the classpath.
• Produces clear failures for missing or invalid resources.
• Adds focused unit, serialization, and provider tests.
• Keeps CAPI enrichment and controller integration outside this ticket’s scope (this will be done as part of another ticket so the PR is not too large)

Screenshots

Not applicable. This PR adds backend contract and provider infrastructure without user-visible changes.

Checklist

• Tested locally
• Will not break dotcom-rendering — payload shape is protected by serialization tests
• No new test data/database files were generated
• Accessibility checks are not applicable because there are no UI changes
  • Screen reader testing not applicable
  • Keyboard navigation testing not applicable
  • Colour contrast testing not applicable

[github-actions]

Deploy build 7527 of dotcom:frontend-all to CODE

All deployment options

• Deploy build 7527 of dotcom:frontend-all to CODE
• Deploy parts of build 7527 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.

[gu-prout]

Seen on FRONTS-PROD, ADMIN-PROD (merged by @gustavo-olmedo 9 minutes and 5 seconds ago)

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