feat: [web app] support both branches and tags in the reference selector

[agriyakhetarpal]

Description

Tip

This change has been made on top of the changes in #261, but is more or less separate from them.

This pull request adds support in the repo-review web app for both branches and tags as refs when selecting a GitHub repository to run the tool on.

Changes made

• Added GitHub API integration to fetch both branches and tags for selected repositories
• The URL parameter handling has been modified to track the reference type. The branches are shown first in the autocomplete dropdown, and tags come later.
• A fallback has been included for common branches when API requests fail (main/develop/stable/etc.)

[agriyakhetarpal]

Question: are there tests for the web app currently? I don't see any at the moment – though I've tested the changes locally, of course.

[henryiii]

Thanks! No, no tests ATM. Ideas welcome.

[henryiii]

The main branch is not on top, would that be possible?

[agriyakhetarpal]

Thanks! No, no tests ATM. Ideas welcome.

It is a tricky case. I would say we shouldn't over-complicate anything – if sp-repo-review and its dependencies work inside a pyodide venv for a simple repository, that should be fine for a start as an integration test of sorts. UI tests with a Selenium runner can come later.

The main branch is not on top, would that be possible?

Yes, I think so. We can have main, stable, and friends show up at the top; the entries are sorted based on how we receive them from GitHub's API and we can treat them as special cases.