- Replace .eslintrc.cjs with eslint.config.mjs (ESLint 9 flat config)
using direct eslint-plugin-solid + @typescript-eslint/parser approach
- Add @typescript-eslint/parser to root devDependencies
- Add main/module/types top-level fields to packages/core/package.json
- Add resolve.conditions to packages/core/vite.config.ts
- Create packages/core/tsconfig.test.json for test type-checking
- Remove empty paths:{} from packages/core/tsconfig.json
