Add a basic linting / code-style config for TypeScript (e.g., eslint)

Min Requirements

• Indentation: 2 spaces
• Very Basic JavaScript/TypeScript rules (whatever eslint offers)
• JavaScript Objects / Attributes: Trailing commas
• Consistent brace style (curly)

Acceptance Criteria

• Code-Style config and dev-dependencies added
• Code is linted and fixed once
• Unused variables and imports are detected/reported
• For every PR, the lint step is executed and fails if the linter detects an error