improvement(next): bundle and CI cache config (#4478)

- drop redundant turbopack config (Next 16 defaults)
- remove lucide-react/date-fns from optimizePackageImports (built-in defaults)
- enable turbopackFileSystemCacheForBuild for warm CI builds
- disable poweredByHeader
- swap actions/cache for Blacksmith sticky disk on .next/cache

.github/workflows/test-build.yml

@@ -44,13 +44,11 @@ jobs:
           key: ${{ github.repository }}-turbo-cache
           path: ./.turbo
 
-      - name: Restore Next.js build cache
-        uses: actions/cache@v5
+      - name: Mount Next.js build cache (Sticky Disk)
+        uses: useblacksmith/stickydisk@v1
         with:
+          key: ${{ github.repository }}-nextjs-cache
           path: ./apps/sim/.next/cache
-          key: ${{ runner.os }}-nextjs-${{ hashFiles('bun.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-nextjs-
 
       - name: Install dependencies
         run: bun install --frozen-lockfile