Refactor login page (#31530)

As requested in
https://github.com/go-gitea/gitea/pull/31504#issuecomment-2196196646.
This PR refactor the login page:

![Screenshot from 2024-07-04
19-23-10](https://github.com/go-gitea/gitea/assets/6918444/c45700f4-6747-473c-bdee-2156718a7953)

![Screenshot from 2024-07-04
19-23-21](https://github.com/go-gitea/gitea/assets/6918444/b1bf71cf-85f9-4517-a409-cc6d72e6af8f)

![Screenshot from 2024-06-30
09-35-20](https://github.com/go-gitea/gitea/assets/6918444/728cc37e-0cca-4883-afec-a43663d2c666)


# Changes
- [x] use separate box for passkey login and go to registration
- [x] move forgot passoword next to password label
- [x] fix password required label `*` and padding 
- [x] remove tabs from login page

---------

Co-authored-by: silverwind <me@silverwind.io>

options/locale/locale_en-US.ini

@@ -387,8 +387,8 @@ relevant_repositories = Only relevant repositories are being shown, <a href="%s"
 
 [auth]
 create_new_account = Register Account
-register_helper_msg = Already have an account? Sign in now!
-social_register_helper_msg = Already have an account? Link it now!
+already_have_account = Already have an account?
+sign_in_now = Sign in now!
 disable_register_prompt = Registration is disabled. Please contact your site administrator.
 disable_register_mail = Email confirmation for registration is disabled.
 manual_activation_only = Contact your site administrator to complete activation.
@@ -396,7 +396,8 @@ remember_me = Remember This Device
 remember_me.compromised = The login token is not valid anymore which may indicate a compromised account. Please check your account for unusual activities.
 forgot_password_title= Forgot Password
 forgot_password = Forgot password?
-sign_up_now = Need an account? Register now.
+need_account = Need an account?
+sign_up_now = Register now.
 sign_up_successful = Account was successfully created. Welcome!
 confirmation_mail_sent_prompt_ex = A new confirmation email has been sent to <b>%s</b>. Please check your inbox within the next %s to complete the registration process. If your registration email address is incorrect, you can sign in again and change it.
 must_change_password = Update your password
@@ -459,6 +460,7 @@ password_pwned = The password you chose is on a <a target="_blank" rel="noopener
 password_pwned_err = Could not complete request to HaveIBeenPwned
 last_admin = You cannot remove the last admin. There must be at least one admin.
 signin_passkey = Sign in with a passkey
+back_to_sign_in = Back to Sign In
 
 [mail]
 view_it_on = View it on %s