test: run part of the component test suite in vitest browser mode

Add a `browser` Vitest project that runs real-browser component tests via Playwright,
alongside the existing jsdom `web` and `node` projects.

- migrate the emotion, ui-a11y-content, ui-a11y-utils, ui-alerts, ui-avatar, ui-badge and
  ui-dialog test suites to browser mode, and delete the Cypress specs they replace
- alias `@instructure/*` workspace packages to TypeScript source so browser tests run
  without a prebuild, and alias bare `moment` to the all-locales build
- exclude the migrated packages from the `web` project so they do not run twice
- add `test:browser`, `test:browser-watch` and `test:browser-ui` scripts
- add a `Vitest browser tests` job to PR validation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: matyasf

.github/workflows/pr-validation.yml

@@ -37,6 +37,24 @@ jobs:
         run: pnpm run bootstrap
       - name: Run vitest unit tests
         run: pnpm run test:vitest
+  vitest-browser-tests:
+    name: Vitest browser tests
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: pnpm/action-setup@v6
+      - uses: actions/setup-node@v6
+        with:
+          node-version: '24'
+          cache: 'pnpm'
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+      - name: Install Playwright browser
+        run: pnpm exec playwright install --with-deps chromium
+      - name: Bootstrap project
+        run: pnpm run bootstrap
+      - name: Run vitest browser tests
+        run: pnpm run test:browser
   cypress:
     name: Cypress component tests
     runs-on: ubuntu-latest

.gitignore

@@ -15,6 +15,7 @@ __build__
 .tmp/
 .pnpm-store/
 .transpile-diff/
+.vitest-attachments/
 
 tsconfig.build.tsbuildinfo
 tsconfig.node.build.tsbuildinfo