fix(ci): integrate regression-test into pnpm workspace and fix Cypress

Major fixes for CI/CD test failures:

1. **Add regression-test to pnpm workspace**:
   - Update pnpm-workspace.yaml to include 'regression-test'
   - Now managing 99 workspace packages (was 98)

2. **Fix regression-test dependencies**:
   - Remove file: protocol dependency ("instructure-ui": "file:../packages")
   - Add proper workspace dependencies:
     - @instructure/emotion: workspace:*
     - @instructure/ui-a11y-content: workspace:*
   - Fixes module resolution errors in visual regression tests

3. **Fix Cypress binary installation**:
   - Add "Install Cypress binary" step in pr-validation.yml
   - Run npx cypress install after pnpm install
   - Fixes "Cypress binary is missing" error

4. **Update lockfile**:
   - pnpm install regenerates lockfile with workspace changes
   - Cypress binary auto-installs via postinstall hook

Fixes:
- Visual regression: "Module not found: Can't resolve '@instructure/emotion'"
- Cypress component tests: "The Cypress binary is missing"

All workspace packages now properly linked and accessible.

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

Co-Authored-By: Claude <[email protected]>

Author: balzss

.github/workflows/pr-validation.yml

@@ -55,6 +55,8 @@ jobs:
           cache: 'pnpm'
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
+      - name: Install Cypress binary
+        run: npx cypress install
       - name: Bootstrap project
         run: pnpm run bootstrap
       - name: Run Cypress components tests