Make search dialog resizable

I see that search dialog design is inspired by VS Code. In VS Code it, however, can be resized horizontally. Please make this also possible in SourceGit.

Also, text placeholder (`Find...`) and button tooltips are not localized:

<img width="1351" height="729" alt="Search dialog" src="https://github.com/user-attachments/assets/37e22845-9445-456a-a283-4a87ac4c6bb8" />