fix: qualify translate/LOCALES references after I18n module refactor

Upstream commit bc64cd9b moved translate / LOCALES into module I18n
(with extend self). The oidc-support branch added new call sites in
login.cr / login.ecr that used the old top-level names; the merge
auto-resolved textually but left the compiler with three undefined
references.

Wrap the new call sites the same way the rest of the codebase already
does: 'I18n.translate(...)' for views and 'I18n::LOCALES' for the
constant.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/invidious/routes/login.cr

@@ -298,7 +298,7 @@ module Invidious::Routes::Login
     end
 
     if language_header = env.request.headers["Accept-Language"]?
-      if language = ANG.language_negotiator.best(language_header, LOCALES.keys)
+      if language = ANG.language_negotiator.best(language_header, I18n::LOCALES.keys)
         user.preferences.locale = language.header
       end
     end

src/invidious/views/user/login.ecr

@@ -7,7 +7,7 @@
     <div class="pure-u-1 pure-u-lg-3-5">
         <div class="h-box">
             <% if CONFIG.auth_type.size > 1 && account_type.empty? %>
-                <h3><%= translate(locale, "Log in") %></h3>
+                <h3><%= I18n.translate(locale, "Log in") %></h3>
                 <p>Choose authentication method:</p>
                 <% if CONFIG.auth_internal_enabled? %>
                     <a href="/login?type=invidious&referer=<%= URI.encode_www_form(referer) %>" class="pure-button pure-button-primary" style="width: 100%; margin-bottom: 10px; display: block; text-align: center; text-decoration: none;">
@@ -22,7 +22,7 @@
             <% else %>
                 <% case account_type when %>
             <% when "oidc" %>
-                <h3><%= translate(locale, "Log in") %></h3>
+                <h3><%= I18n.translate(locale, "Log in") %></h3>
                 <p>Select an OIDC provider to log in:</p>
                 <% CONFIG.oidc.each do |provider_key, provider| %>
                     <form class="pure-form" action="/login?referer=<%= URI.encode_www_form(referer) %>&type=oidc" method="post">