chore: migrate unit test runner from Jest to Vitest

[Quramy]

Summary

• Replace Jest (30.2.0) + ts-jest with Vitest for unit testing
• Vitest provides native TypeScript support via esbuild, eliminating the ts-jest dependency
• All 33 test files (424 tests) pass successfully

Changes

• Dependencies: Remove jest, ts-jest, @types/jest; add vitest, @vitest/coverage-v8
• Config: Replace jest.config.mjs with vitest.config.ts (includes resolve aliases for tsmodule and graphql)
• Test files: Replace jest.fn() with vi.fn() in 6 files
• Snapshots: Regenerated all snapshots in Vitest format
• Scripts: jest → vitest, jest:ci → vitest:ci, watch:jest → watch:vitest
• CI: Update codecov step name in build.yml

Test plan

• npx vitest run passes all 424 tests
• npx vitest run --coverage generates coverage report at coverage/coverage-final.json
• CI build passes with codecov upload

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.05%. Comparing base (a8bdb2e) to head (05c90b0).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1565      +/-   ##
==========================================
- Coverage   96.52%   92.05%   -4.48%     
==========================================
  Files          80       78       -2     
  Lines        5964     5777     -187     
  Branches     1195     1052     -143     
==========================================
- Hits         5757     5318     -439     
- Misses        200      459     +259     
+ Partials        7        0       -7     

see 62 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.