type (shared): Implement Git Diff Viewer

[jonasyr]

This can be developed independently, though it would integrate best with the Git Graph Timeline (Issue #43 ). Consider working on this after or alongside Issue #43 for optimal integration.

🧾 Beschreibung

Create a diff viewer that shows code changes when clicking on a commit or file. This will give users a better understanding of what changed in each commit.

🛠 Umsetzungsschritte

• Add backend endpoint to retrieve file diffs
• Implement a syntax-highlighted diff viewer component
• Add navigation between files in a commit
• Implement collapsible sections for changed files
• Add line-by-line and side-by-side diff viewing options
• Create keyboard shortcuts for navigating diffs

🗂 Labels

• scope:frontend
• scope:backend
• type:feature
• prio:medium

📁 Code Ort(e)

• apps/backend/src/services/gitService.ts (add diff retrieval function)
• apps/frontend/src/components/DiffViewer.tsx (new component)
• apps/frontend/src/utils/diffFormatter.ts (formatting utils)