chore: bump next for example app

[zhukaihan]

Summary

Bump next js version to fix vulnerability.

Checklist

• Does your PR title have the correct title format?
• Does your PR have a breaking change?: no

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Note

Medium Risk
Upgrades the ssr-demo app’s framework/runtime dependencies (Next.js and transitive build tooling), which can introduce subtle build/runtime behavior changes despite being a version bump.

Overview
Updates the ssr-demo example app to use Next.js ^13.5.9 (lockfile resolves to 13.5.11), replacing the prior 13.3.0 stack.

Regenerates yarn.lock accordingly, pulling in newer Next-related SWC binaries and associated dependency bumps (notably postcss, nanoid, and watchpack).

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[Copilot]

Pull request overview

Updates the ssr-demo example app’s Next.js dependency to pick up security/patch fixes while keeping changes scoped to the demo workspace.

Changes:

• Bumped next in packages/ssr-demo from ^13.3.0 to ^13.5.9.

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