- Add vitest.config.mts with happy-dom environment and path aliases
- Add src/test/setup.ts to register @testing-library/jest-dom matchers
- Add test:unit script to package.json
- Add vitest.config.mts to tsconfig.json include for ESLint compatibility
- Remove redundant test devDependencies already declared at root
- Add 132 tests across 16 files covering stores, composables, utils, and constants
