Fix lint, production audit, and starter docs

[shelajev]

Summary

• make npm run lint pass by adding service-worker globals, scoping the Fast Refresh export rule away from context modules, and removing unused markdown renderer props
• bump react-router to ^8.3.0 to clear the production dependency audit finding
• update agent docs to point authors at dockersamples/simspace-starter instead of the removed template/ directory

Verification

• npm ci
• npm run validate-lab -- public/lab
• npm run validate-lab -- ../../simspace-starter/lab
• npm run lint
• npm run build
• npm audit --omit=dev
• npx prettier --check AGENTS.md app/eslint.config.js app/package.json app/src/components/WorkshopPanel/markdown/MarkdownRenderer.jsx app/src/components/WorkshopPanel/markdown/RenderedImage.jsx app/src/components/WorkshopPanel/markdown/RenderedSvg.jsx app/src/components/WorkshopPanel/markdown/VariableDefinition.jsx app/src/components/WorkshopPanel/markdown/VariableSetButton.jsx