Add a way to import character into a new loadout

[xoxorwr]

Fixes # .

Description of the problem being solved:

This drastically simplify the process of importing/managing your actual character when following a build guide.

I also took the opportunity to refine the import UI.

Steps taken to verify a working solution:

• I tested both import modes (oauth&name), and made sure they correctly import data
• I made sure it properly give a warning in case of overwriting an existing loadout

Link to a build that showcases this PR:

Before screenshot:

After screenshot:

2026-07-29.17-26-03.mp4

I'm submitting this as a draft because I'm not happy with the code, the original code had bunch of duplicated widgets to handle both import modes, so I had to work with that in mind, I'm thinking of rewriting the whole module from scratch, but it's kind of a daunting task, I'll think about it more on a later date.

[vaisest]

What's the idea behind this? Wouldn't you normally import your build normally and then import the guide build as a comparison?

I do welcome any import UI change attempts, though. It ended up feeling sort of duplicated imo. But it seems like the default is site import here? I don't think that's ideal since bandit choices are oauth-only. There are also some differences which could be useful in the future like items having mod ids and the AG items