Feat: remember last identity provider on login

[PreciousOritsedere]

Summary

Remembers the last Solid identity provider URL in localStorage and prefills the login field with it on the next visit, so returning users don't have to re-enter their provider.

Closes #39

Test plan

• Log in with a provider, log out → login field is prefilled with that provider
• Log in with a different provider → prefill updates to the new one
• Login still works with the preset options and custom URLs

[jeswr]

I would keep this file named as just LoginPage the fact that it remembers the IDP is just a feature of the page.

[PreciousOritsedere]

I have pushed a commit for this

[jeswr]

We should be aiming to get the "remember last identity provider" feature upstreamed to the reactive authentication library; and to migrate to that library here.

[PreciousOritsedere]

We should be aiming to get the "remember last identity provider" feature upstreamed to the reactive authentication library; and to migrate to that library here.

Yes I plan to do this subsequently