feat: add @ for dirs references

What version of the VS Code extension are you using?

current latest

Which IDE are you using?

vscode

What platform is your computer?

macos

What steps can reproduce the bug?

Not a bug, but feature/improvement.

Please add ability to reference via @ dirs, in agent input box
for example @src @test
also i think it would be good to render the name as full relpath, not only file name
for example @src/main.py rather than @main.py

What is the expected behavior?

_No response_

What do you see instead?

_No response_

Additional information

_No response_