[Blueprints] Allow WXR imports to preserve source URLs

[adamziel]

What?

Adds a rewriteUrls option to the importWxr step.

rewriteUrls	Behavior
true or omitted	Keep the current behavior: ask the WXR importer to rewrite imported URLs to the current Playground site URL.
false	Preserve URLs from the WXR file.

The public Blueprint schema is regenerated to include the new option.

Why?

The WXR importer already performs URL rewriting with awareness of WXR content instead of doing raw string replacement over SQL. Blueprint v2 needs this control so imports can choose whether remote content URLs are migrated to the current site or preserved as source URLs.

SQL dump URL replacement is intentionally not included here. That needs a structured-data approach rather than raw SQL text replacement.

Testing

• npm exec nx run playground-blueprints:test:vite -- --testFiles=packages/playground/blueprints/src/tests/steps/import-wxr.spec.ts
• npm exec nx run playground-blueprints:typecheck
• npm exec nx run playground-blueprints:lint
• npm exec nx run playground-blueprints:build:blueprint-schema
• npm run format:uncommitted
• git diff --check

Part of #2592.