Use TypeScript 5 for backend build in CI

TypeScript 4.3 can't parse newer type syntax in @types/babel__traverse.
Install TS5 temporarily for the build step.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Laoujin

.github/workflows/playwright.yml

@@ -67,7 +67,10 @@ jobs:
 
       - name: Build backend
         working-directory: ./confac/backend
-        run: npx tsc -p . --skipLibCheck
+        run: |
+          # Use newer TypeScript to handle newer type syntax in dependencies
+          npm install -D typescript@5 --no-save
+          npx tsc -p . --skipLibCheck
 
       - name: Start backend
         working-directory: ./confac/backend