[Website] Add Blueprint bundle resource path helper

[adamziel]

What it does

Adds collectBlueprintBundleResourcePaths(), a helper that finds the files a Blueprint bundle must keep alongside blueprint.json before the bundle is edited. This will come handy for editing Blueprint bundles later on in the Dock UI work.

The helper covers:

• Blueprint v1 { resource: "bundled" } references anywhere in the declaration
• Blueprint v2 execution-context references in themes, plugins, media, content, fonts, post types, and additional steps

Related to #3965.

Other changes

This PR also records the path-handling rule in AGENTS.md: use existing @php-wasm/util path helpers instead of ad-hoc regex/string parsing.

Testing instructions

npm exec nx test playground-website --testFile=blueprint-bundle-resource-paths.spec.ts
npm exec nx lint playground-website
npm exec nx typecheck playground-website

[Copilot]

Pull request overview

Note

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

Adds reusable Blueprint editor helper utilities to (a) collect bundle-backed resource paths from Blueprint v1/v2 shapes and (b) persist updated blueprint.json into bundle-backed filesystem metadata, with accompanying Vitest coverage.

Changes:

• Added helper to write blueprint.json back into a WritableFilesystemBackend-backed originalBlueprint.
• Added helper to collect bundle resource paths across Blueprint v1 (“bundled”) and Blueprint v2 execution-context references (with v2 .. escape rejection).
• Added Vitest specs for bundle-path collection and filesystem writes.

Reviewed changes

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

File	Description
packages/playground/website/src/components/blueprint-editor/blueprint-filesystem.ts	Adds filesystem-backend type guard + helper to write updated blueprint JSON back into bundle metadata.
packages/playground/website/src/components/blueprint-editor/blueprint-filesystem.spec.ts	Tests that the helper writes /blueprint.json only for filesystem-backed originals.
packages/playground/website/src/components/blueprint-editor/blueprint-bundle-resource-paths.ts	Adds traversal/collection of bundle resource paths for Blueprint v1 and v2 structures.
packages/playground/website/src/components/blueprint-editor/blueprint-bundle-resource-paths.spec.ts	Tests v1 bundled path collection, v2 execution-context collection, and v2 parent-directory escape rejection.

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