chore(test): normalize test setup — upgrade Vitest to 3.x, fix CI hang

- Fix "test" script: vitest (watch mode, hangs CI) → vitest run
- Add "test:watch": "vitest" script
- Upgrade vitest and @vitest/coverage-v8 from ^1.6.1 to ^3.2.4
- Bump typedoc to ^0.28.17 and typedoc-plugin-markdown to ^4.10.0 (TS 5.9 compat)
- Align vitest.config.ts to standard template (keep singleThread for WS port conflicts)
- Delete dead jest.config.js and tsconfig.test.json
- All 16 tests pass

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vveerrgg