ci: remove redundant Bun setup from PR checks

.github/workflows/pr-checks.yml

@@ -69,9 +69,6 @@ jobs:
       - name: Setup Node.js and pnpm
         uses: ./.github/actions/setup-node-pnpm
 
-      - name: Install Bun
-        uses: oven-sh/setup-bun@v2
-
       - name: Build
         run: pnpm build
 
@@ -94,9 +91,6 @@ jobs:
       - name: Setup Node.js and pnpm
         uses: ./.github/actions/setup-node-pnpm
 
-      - name: Install Bun
-        uses: oven-sh/setup-bun@v2
-
       # Dist-artifact cache (same contract as full-suite.yml): exact-match
       # key only, NO restore-keys (stale dist is the known failure mode,
       # FN-4232/FN-4605), NEVER node_modules (breaks Windows pnpm junctions).