[WIP] Update express dependency to version ^5.2.1

[Copilot]

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Original prompt

Update the express dependency in t/backend/package.json to the latest stable version.

Current state

File: t/backend/package.json

"dependencies": {
  "express": "^4.22.1"
}

Required change

Update express to ^5.2.1 (latest stable as of 2026).

Note: Express 5.x requires Node.js 18 or higher. Please also check if there are any other files in the t/backend/ directory (e.g., index.js, package-lock.json) that may need adjustments for the Express 5.x upgrade (e.g., API breaking changes such as error handling, path routing, or async middleware).

Please update t/backend/package.json and any other affected files as needed.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: update all packages in package.json

Assistant: We're waiting for your response to the confirmation dialog to proceed with creating the pull request that updates express from ^4.22.1 to ^5.2.1 in t/backend/package.json.

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