Allow selecting directories in @ file search

What feature would you like to see?

Problem: @ file search in Composer popup only shows files.

Use-Case: When working with a codebase, being able to reference an entire directory (e.g., a library, module, or package) is crucial, models are good enough to do List/Ls and then rg or Read any files they want. Also, not to mention selecting a handful of relevant files one by one takes A LOT of time.

Solution: Show directories in @ search results with a trailing "/" suffix (e.g., "src/utils/"). When selected, the directory path is inserted, allowing the agent to understand which directory the user is referencing.

Additional information

I have a working implementation ready:

• Adds "/" suffix to directories in file search results

<img width="1703" height="575" alt="Image" src="https://github.com/user-attachments/assets/3a19d28d-63f3-4899-992e-66f3439e6d7b" />

• Allows selecting directories just like files

<img width="1703" height="575" alt="Image" src="https://github.com/user-attachments/assets/2b6a9741-1b5d-49fc-a007-36c203450f19" />

Happy to submit a PR once this enhancement is approved