feat: add local datetime support and automated updated_at trigger for items table

Add comprehensive test suite (35 tests) and update journal ...

- Create test/ folder with 5 test modules (35 tests total)
  * db.test.js: Database operations (5 tests)
  * mcp-tools.test.js: Tool definitions (11 tests)
  * mcp-handlers.test.js: Handler implementation (6 tests)
  * llama-client.test.js: LLama API integration (9 tests)
  * integration.test.js: End-to-end workflows (4 tests)
- Add test/setup.js: Shared test utilities
- Add test/README.md: Test documentation
- Update package.json: Add test scripts (7 variants)
- Update journals/20260206-0000-案件.md: Document test implementation
- All 35 tests passing (139 expect calls)