[Feature] Add intercepts target capability support

[henryStelle]

Resolves https://github.com/shop/issues-retail/issues/33526
Depends on: https://meteorite.shopify.io/repos/shop/world/pulls/2005826

WHY are these changes introduced?

UI extension target configurations currently recognize only allow_direct_linking under target capabilities, so intercepts declarations are not retained when the configuration is parsed.

WHAT is this pull request doing?

• Adds support for the optional intercepts UI extension target capability.
• Preserves the existing typed validation for allow_direct_linking.
• Adds coverage that verifies nested intercepts configuration is retained through parsing and transformation.
• Adds a minor changeset for @shopify/app.

Schema note

intercepts intentionally accepts a loosely typed payload during limited testing so the configuration contract can evolve without coupling iteration to CLI releases. This form will not be publicly documented. Before broader availability and public documentation, we plan to replace it with a stricter schema that reflects the finalized contract.

How to test your changes?

• ✅ dev test packages/app/src/cli/models/extensions/specifications/ui_extension.test.ts — 53 tests passed
• ✅ dev lint
• ✅ dev type-check
• ✅ Focused Prettier check
• ✅ git diff --check

Checklist

• I've considered possible cross-platform impacts (schema-only change)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type and added a minor changeset