[FEATURE]: replace external GUI cloning tools with desktop clone flow

[anduimagui]

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

It would be great to be able to replace GUI cloning tools like GitHub Desktop entirely, allowing quick investigation and checkout of new repositories through the OpenCode desktop interface.

Today the workflow still relies on an external GUI cloning tool, then returning to OpenCode. A built-in clone flow in the desktop app would make it possible to stay inside OpenCode for the whole repo discovery and checkout process.

A few behavior ideas worth considering:

• keep Command-Shift-O as a fast way to open the clone dialog
• or move cloning to the command palette if we want to reserve that shortcut for something more important later
• accept full git URLs and shorthand forms like github.com/org/repo
• suggest a sensible local destination and let the user adjust it before cloning

I'm open to suggestions on the best behavior, but the main goal is to make OpenCode capable enough that GitHub Desktop is no longer needed for this workflow.