chore: deploy health check fix, TS 6 compat, and dep pins

[vpatrin]

Summary

• Fix deploy health check — use docker inspect instead of curl localhost:3000 which can't reach containers on the internal Docker network
• Add CSS type declaration (src/css.d.ts) for TypeScript 6 compatibility (unblocks PR chore(deps-dev): bump typescript from 5.9.3 to 6.0.2 #6)
• Pin next, eslint-config-next, and @react-three/fiber in dependabot to avoid breaking upgrades
• Bump React 19.2.4→19.2.5, add react-use-measure (R3F 9.5 peer dep)

Changes

• deploy.yml — health check uses docker inspect --format='{{.State.Health.Status}}' + docker logs on failure
• dependabot.yml — ignores next, eslint-config-next, @react-three/fiber
• src/css.d.ts — declare module "*.css" for TS 6
• package.json / yarn.lock — React patch bump, react-use-measure added

How to test

1. yarn build passes
2. npx -p typescript@6 tsc --noEmit passes
3. Deploy and verify health check step succeeds