TypeScript monorepo migration

[epatey]

Summary

• Moves the scout frontend into a separate TypeScript monorepo (Turborepo + pnpm workspaces), referenced as a git submodule at src/inspect_scout/_view/frontend/
• Updates Python server to serve from _view/dist/ (built by submodule) instead of _view/www/dist/
• Splits CI: frontend lint/typecheck/test/e2e runs in the TS monorepo repo; Python repo CI validates three sync points (stories 8–10): mismatched openapi.json, mismatched generated.ts, and mismatched dist/
• Moves npm-publish.yml back to Python repo, with submodule checkout and publish-time package identity patching
• Adds design documents: monorepo plan, walkthroughs for UI-only and coordinated API+UI changes