Drag and Drop for files in chats

**Is your feature request related to a problem? Please describe.**
Uploading files in Nextcloud Talk currently requires multiple clicks and selecting files manually through the Finder/Files app.

**Describe the solution you'd like**
Files should be uploadable via Drag and Drop (dragging and dropping them directly into the chat window), making the process faster and more intuitive.

**Describe alternatives you've considered**
- Using the existing upload button.

**Additional context**
Drag-and-drop for file upload is a standard feature in modern chat tools and would significantly improve the user experience.