project panel: Add git clone action to empty state (#36371)

This PR adds the git clone action to the project panel. It also changes
the "open" button to open a folder instead of the recent projects modal,
which feels faster to start with, more intuitive, and also consistent
with VS Code (which I think is good in this specific case).

<img width="500" height="1334" alt="CleanShot 2025-08-17 at 2  10 01@2x"
src="https://github.com/user-attachments/assets/ff953228-9e8e-413b-89ba-fa0870a0df17"
/>

Release Notes:

- Improved the project panel empty state by including the git clone
action and allowing users to quickly open a local folder.

crates/onboarding/src/welcome.rs

@@ -37,7 +37,7 @@ const CONTENT: (Section<4>, Section<3>) = (
             },
             SectionEntry {
                 icon: IconName::CloudDownload,
-                title: "Clone a Repo",
+                title: "Clone Repository",
                 action: &git::Clone,
             },
             SectionEntry {