[Website] Create blueprint.json for editable Blueprints that have none

[adamziel]

This PR creates a minimal blueprint.json when an editable Blueprint has none.

The Blueprint editor always reads /blueprint.json. An editable Blueprint with no declaration or a bundle with no file leaves the editor with nothing to open.

Create a minimal blueprint.json when an editable filesystem does not have one. Do not write the file when reading a stored, read-only bundle.

This gives the Blueprint editor a file to open when it moves into the Dock in #3965.

Verified with npm exec nx test playground-website --output-style=static and npm exec nx typecheck playground-website --output-style=static.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Seeds editable Blueprint bundles with a minimal blueprint.json so the Blueprint editor always has a file to open, while avoiding mutation of persisted/read-only bundles during inspection.

Changes:

• Added a minimal stub blueprint.json and logic to ensure it exists for editable/in-memory filesystems.
• Updated filesystem creation to optionally seed missing blueprint.json depending on caller/read-only context.
• Added Vitest coverage for readSiteBlueprintJson seeding and non-mutation behavior.

Reviewed changes

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

File	Description
packages/playground/website/src/components/blueprint-editor/SiteBlueprintBundleEditor.tsx	Adds stub blueprint seeding + optional behavior to avoid mutating persisted bundles when reading.
packages/playground/website/src/components/blueprint-editor/SiteBlueprintBundleEditor.spec.ts	Adds tests validating stub seeding and that reading doesn’t write into a filesystem backend.

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