fix: make StackBlitz startup WebContainer-safe - #19

Summary

• replace the StackBlitz startup path that invoked Turbo's unsupported native binary with an ordered pnpm workspace build
• point .stackblitzrc and every GitHub/Pages live-lab link at dev:stackblitz
• include the WebContainer-safe build in pnpm check so the path remains release-gated
• record the post-release fix under Unreleased without moving or rewriting v1.0.0-beta.2

Reproduction

The deployed live-lab link imported the repository, then failed in StackBlitz WebContainers at turbo run build with reached EOF without closing quote from the native Turbo binary.

Validation

• moved every packages/*/dist away, then pnpm build:stackblitz rebuilt all nine packages successfully in dependency order
• pnpm dev:stackblitz reached a ready Vite 8 development server locally
• CAUSESCOPE_DOCS_BASE=/causescope/ pnpm docs:build
• all four live-lab URLs decode to the existing dev:stackblitz script
• independent review completed with no remaining findings

After merge

• verify the Pages CTA uses the new URL
• re-import the default branch in StackBlitz and confirm the pnpm build completes and Vite preview starts