fix: add npm install step to deploy-preview job

- Add "npm ci" before building in deploy-preview job
- This fixes "next: not found" error when vercel build falls back to npm run build
- Dependencies are now installed before attempting to build the project

The error occurred because:
1. Vercel build failed (VERCEL_TOKEN not configured)
2. Fallback to npm run build was triggered
3. But dependencies were never installed, causing "next: not found"

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

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

Author: rishabh3562

.github/workflows/ci-cd-pipeline.yml

@@ -321,6 +321,9 @@ jobs:
           node-version: ${{ env.NODE_VERSION }}
           cache: 'npm'
 
+      - name: Install dependencies
+        run: npm ci --prefer-offline
+
       - name: Install Vercel CLI
         run: npm install --global vercel@latest