fix: ux issues in project open workflows when path doesnt exist

[abose]

1. If we switch project and path doesn't exist, then we used to switch to the default project which is not expected. Now if path doesn't exist, we show an error dialog and not switch from the current project.
2. Project error messages shown to user was virtual /tauri or /fs or /mnt/, ie vfs paths. Now we resolve to a user readable path.
3. update readme
4. also add sass variables test case in color gutter tests.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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