feat: show "Comments are turned off" message when YouTube comments are disabled

Closes #1092

- Detect messageRenderer in YouTube API response when comments are disabled
- Show a localized "Comments are turned off" message in HTML response
- Add "commentsDisabled: true" flag to both JSON and HTML API responses
- Add I18n locale string for the disabled message
- Handle both empty continuationItems and messageRenderer presence

locales/en-US.json

@@ -238,6 +238,7 @@
     "This channel does not exist.": "This channel does not exist.",
     "Could not get channel info.": "Could not get channel info.",
     "Could not fetch comments": "Could not fetch comments",
+    "Comments are turned off": "Comments are turned off",
     "comments_view_x_replies": "View {{count}} reply",
     "comments_view_x_replies_plural": "View {{count}} replies",
     "`x` ago": "`x` ago",

src/invidious/comments/youtube.cr

@@ -94,17 +94,45 @@ module Invidious::Comments
 
     if !contents
       if format == "json"
-        return {"comments" => [] of String}.to_json
+        return {
+          "comments"         => [] of String,
+          "commentCount"     => 0,
+          "commentsDisabled" => true,
+        }.to_json
       else
-        return {"contentHtml" => "", "commentCount" => 0}.to_json
+        return {
+          "contentHtml"      => Frontend::Comments.template_youtube_disabled(locale),
+          "commentCount"     => 0,
+          "commentsDisabled" => true,
+        }.to_json
       end
     end
 
     continuation_item_renderer = nil
+    has_message_renderer = false
     contents.as_a.reject! do |item|
       if item["continuationItemRenderer"]?
         continuation_item_renderer = item["continuationItemRenderer"]
         true
+      elsif item["messageRenderer"]?
+        has_message_renderer = true
+        true
+      end
+    end
+
+    if has_message_renderer || contents.as_a.empty?
+      if format == "json"
+        return {
+          "comments"         => [] of String,
+          "commentCount"     => 0,
+          "commentsDisabled" => true,
+        }.to_json
+      else
+        return {
+          "contentHtml"      => Frontend::Comments.template_youtube_disabled(locale),
+          "commentCount"     => 0,
+          "commentsDisabled" => true,
+        }.to_json
       end
     end
 

src/invidious/frontend/comments_youtube.cr

@@ -1,6 +1,14 @@
 module Invidious::Frontend::Comments
   extend self
 
+  def template_youtube_disabled(locale)
+    <<-END_HTML
+    <div class="h-box">
+      <p>#{I18n.translate(locale, "Comments are turned off")}</p>
+    </div>
+    END_HTML
+  end
+
   def template_youtube(comments, locale, thin_mode, is_replies = false)
     String.build do |html|
       root = comments["comments"].as_a