Dockerfile: set vscode user in both tsffs dev and prod images

[Wenzel]

No description provided.

[Copilot]

Pull Request Overview

This PR updates the Dockerfile to set a consistent vscode user in both development and production images for the TSFFS project. The changes create a unified user management approach and reorganize the build stages for better maintainability.

• Introduces a new create-user base stage that creates the vscode user with proper permissions
• Restructures both tsffs-dev and tsffs-prod stages to inherit from the new user creation stage
• Adds aggressive cleanup to CI workflow to free up disk space during builds

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
Dockerfile	Restructures multi-stage build to create vscode user in both dev and prod images, consolidates user creation logic, and fixes file permissions
.github/workflows/ci.yml	Adds aggressive cleanup step to remove unused software packages and free disk space

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