chore: migrate test infrastructure from Jest to Vitest (#3047)

## Summary

- **Migrate test infrastructure from Jest to Vitest** — replace Jest,
Babel, and all related config with Vitest 4.x powered by the native Vite
pipeline
- **Rename JSX test files to `.jsx`** — 111 test files + 19 snapshot
files renamed so Vite handles JSX natively, eliminating the custom
`jsxInJs` esbuild plugin
- **Remove legacy example apps** — delete `capacitor`, `nextjs`, and
`website-demos` examples (keeping only `vite` and `tutorial`)
- **Remove E2E/Ladle infrastructure** — delete Playwright E2E tests,
Ladle stories, and all related config
- **Tidy ESLint config** — migrate to flat config, remove Jest plugin,
add Vitest plugin
- **Restore Codecov integration** — add the missing
`codecov/codecov-action` upload step to CI
- **Clean up unused dependencies** — remove `@axe-core/react`,
`@types/dotenv`, `@types/uuid`, `@types/deep-equal`, `@types/moment`,
`@types/textarea-caret`, `@types/lodash.defaultsdeep`, `autoprefixer`,
`dotenv`
- **Update GitHub Actions** — `actions/checkout` v4→v6,
`actions/setup-node` v4→v6, `actions/cache` v4→v5

### Details

**Test migration**:
- All `jest.fn()` / `jest.spyOn()` → `vi.fn()` / `vi.spyOn()`
- `jest.mock()` → `vi.mock()` with `async importOriginal` pattern
- Replaced `jest.useFakeTimers()` / `jest.useRealTimers()` with Vitest
equivalents
- Updated timer advancing (`jest.advanceTimersByTime` →
`vi.advanceTimersByTime`, etc.)
- Fixed `mockImplementation()` no-arg calls that behave differently in
Vitest (→ `mockResolvedValue()`)
- Setup file: `jest.env.setup.js` → `vitest.setup.ts` with
`@testing-library/jest-dom/vitest` and `vitest-axe`
- Coverage: v8 provider scoped to `src/**/*.{ts,tsx,js,jsx}`, excludes
`@types`, tests, mock-builders

**JSX file rename**:
- Renamed 111 `.test.js` → `.test.jsx` and 19 `.test.js.snap` →
`.test.jsx.snap`
- Removed custom `jsxInJs()` esbuild pre-transform plugin from
`vitest.config.ts`
- Vite now handles JSX natively via file extension — no double-transform
overhead

**Removed configs**: `.babelrc.js`, `babel.config.js`, `jest.config.js`,
`jest-global-setup.js`, `assetsTransformer.js`, `playwright.config.ts`,
`tsconfig.test.json` (simplified)

## Test plan

- [ ] `yarn test` — all unit tests pass with no unhandled errors
- [ ] `yarn coverage` — generates coverage report with correct file
scoping
- [ ] `yarn lint` — no lint errors
- [ ] `yarn types` — TypeScript passes
- [ ] `yarn build` — build succeeds
- [ ] CI workflow runs tests and uploads coverage to Codecov

Author: oliverlaz

.babelrc.js

@@ -11,7 +11,7 @@ runs:
   using: 'composite'
   steps:
     - name: Setup Node
-      uses: actions/setup-node@v4
+      uses: actions/setup-node@v6
       with:
         node-version: ${{ inputs.node-version }}
 
@@ -20,7 +20,7 @@ runs:
       run: echo "NODE_VERSION=$(node --version)" >> $GITHUB_ENV
 
     - name: Cache dependencies
-      uses: actions/cache@v4
+      uses: actions/cache@v5
       with:
         path: ./node_modules
         key: ${{ runner.os }}-${{ env.NODE_VERSION }}-modules-${{ hashFiles('./yarn.lock') }}

.github/actions/setup-node/action.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     name: TypeScript
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: ./.github/actions/setup-node
 
@@ -18,21 +18,24 @@ jobs:
     runs-on: ubuntu-latest
     name: Lint & test with Node
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: ./.github/actions/setup-node
 
       - name: Build SDK
         run: yarn build
 
       - name: 🧪 Lint and test with Node ${{ env.NODE_VERSION }}
-        env:
-          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
         run: |
           yarn lint
           yarn coverage
           yarn validate-translations
 
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+
       - name: 🧪 Validate CommonJS bundle with Node ${{ env.NODE_VERSION }}
         run: yarn validate-cjs
 
@@ -45,7 +48,7 @@ jobs:
       VITE_STREAM_API_KEY: ${{ vars.VITE_STREAM_API_KEY }}
       NODE_ENV: production
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: ./.github/actions/setup-node
         env:

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
   pr-title:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: ./.github/actions/setup-node
 

.github/workflows/e2e.yml

@@ -21,7 +21,7 @@ jobs:
     if: ${{ inputs.dry_run || startsWith(github.ref_name, 'release') || startsWith(github.ref_name, 'master') || startsWith(github.ref_name, 'rc')}}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.github/workflows/pr-check.yml

@@ -5,7 +5,7 @@ on:
     branches:
       - master
     paths-ignore:
-      - '**.test.js'
+      - '**.test.*'
       - '**.md'
 env:
   NODE_OPTIONS: --max_old_space_size=4096
@@ -14,7 +14,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: preactjs/compressed-size-action@v2
         env:
           NODE_OPTIONS: --max_old_space_size=4096