chore(deps): bump vite to v8, vite-plugin-svelte to v7, GH Actions to v6 (#11)

- vite: ^6.3.6 → ^8.0.0 (uses Rolldown engine)
- @sveltejs/vite-plugin-svelte: ^5.0.3 → ^7.0.0
- actions/checkout: v4 → v6
- actions/setup-node: v4 → v6
- actions/configure-pages: v4 → v6
- Migrate rollupOptions.treeshake:'safest' to rolldownOptions.treeshake:false
  (Rolldown no longer accepts string preset; false preserves cubejs static-method
  side-effects needed at runtime)

Supersedes dependabot PRs #3, #4, #5, #9, #10.

.github/workflows/deploy.yml

@@ -21,15 +21,15 @@ jobs:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: pnpm/action-setup@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: '24'
           cache: 'pnpm'
       - run: pnpm install --frozen-lockfile
       - run: pnpm build
-      - uses: actions/configure-pages@v4
+      - uses: actions/configure-pages@v6
       - uses: actions/upload-pages-artifact@v5
         with:
           path: dist