perf: cut cold route compilation and unblock preview images (#6441)

.github/workflows/ci.yml

@@ -82,7 +82,7 @@ jobs:
         run: cp .env.example .env
 
       - name: Lint, typecheck, and build affected workspaces
-        run: pnpm turbo run lint typecheck build --affected --continue=dependencies-successful
+        run: pnpm turbo run lint typecheck build --affected --continue=dependencies-successful --concurrency=2
 
       - name: Validate workspace configuration
         run: pnpm lint:ws