Add `fenn pull` command into dashboard

[ApusBerliozi]

We need to have an opportunity to:

1 - Get all available templates as list
2 - Setting a directory, to which a template will be downloaded (with creating non-existing one, or overriding)
3 - Download the template, with progress (and result) shown in the dashboard
4 - Display fenn.yaml and main.py in the dashboard

The main point is to make ML-related job as easy as possible for a user, who has no idea how to work with CLI and other computer-science stuff.

[sarkarshrayan2-max]

Hi, I’d like to work on this issue.

I propose starting with a small backend-focused PR that:

• adds an API endpoint for listing available templates
• adds an API endpoint for downloading a selected template
• supports the target directory and force-overwrite options
• returns structured success and error responses
• includes unit tests using mocked GitHub requests and temporary directories

After that, the dashboard UI and file preview can be added either in the same issue or as a follow-up PR.

Please let me know whether this scope works for you.

[ApusBerliozi]

Hey @sarkarshrayan2-max!

Yeah, your approach is absolutely correct! You can open issues regarding each PR, and I will link them to this one

[sarkarshrayan2-max]

Thanks for confirming.

I have opened #258 for the backend implementation, covering template listing, template downloading, target-directory selection, force overwrite, structured responses, and tests.

After this PR is reviewed, I will open separate follow-up issues for:

1. Dashboard UI integration with download progress and result display
2. Displaying fenn.yaml and main.py in the dashboard

[sarkarshrayan2-max]

Thanks for confirming the split approach.

I opened the backend implementation in #258.

I also opened separate follow-up issues for:

• dashboard template-download UI: Add template download UI to dashboard #259
• fenn.yaml and main.py preview: Display fenn.yaml and main.py in dashboard #260

These together cover the remaining work for #246.