feat: Make it more visible that user invites can be accepted by logging in, in addition to signing up

[rolodato]

When a user opens an invite link, by default they are prompted to sign up, which is the most likely course of action. If a user was previously removed from an organisation, or they already belong to a different organisation, they need to log in instead of signing up.

There is a prompt to log in, but it is difficult to see at the bottom of the page. I've had to explain too many times that this is an option - it makes more sense to offer it as an option before showing the sign up fields.

Lastly, "login" is a noun and not a verb. "Log in" is the correct phrasal verb.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
flagsmith-frontend-preview	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 5, 2025 11:34pm
flagsmith-frontend-staging	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 5, 2025 11:34pm

1 Skipped Deployment

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[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-5077	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-5077	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-5077	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-5077	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-5077	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-5077	Finished ✅	Results ✅

[github-actions]

Uffizzi Preview deployment-60665 was deleted.