votes: fixup various minor issues.

* Add a gap between thumbnails on mobile.
* Adjust CSS for scores and vote buttons.
* Include "Private favorites" as an incentive on the user upgrade page.
* Fix vote buttons not being visible beneath thumbnails on mobile.
* Fix the "Show scores" link not preserving the current page number.
* Fix vote buttons being unintentionally enabled for all thumbnails by default.
* Fix banned and restricted users being able to favorite posts by
  tagging them with `fav:self`.
* Fix search engines being able to crawl /posts?view=score pages.
* Fix broken tests.

app/components/post_preview_component/post_preview_component.html.erb

@@ -55,8 +55,8 @@
       <% end %>
     </p>
   <% elsif show_votes -%>
-    <p class="desc">
+    <div class="post-preview-score text-sm mt-1">
       <%= render_post_votes post, current_user: current_user %>
-    </p>
+    </div>
   <% end -%>
 <% end -%>

app/components/post_preview_component/post_preview_component.scss

@@ -1,12 +1,10 @@
 @import "../../javascript/src/styles/base/000_vars.scss";
 
 article.post-preview {
-  width: 154px;
-  margin: 0 10px 10px 0;
   text-align: center;
   display: inline-block;
   position: relative;
-  vertical-align: top;
+  overflow: hidden;
 
   a {
     display: inline-block;
@@ -119,38 +117,16 @@ body[data-current-user-can-approve-posts="true"] .post-preview {
   }
 }
 
-@media screen and (max-width: 660px) {
+@media screen and (min-width: 660px) {
   article.post-preview {
-    margin: 0;
-    text-align: center;
-    vertical-align: middle;
-    display: inline-block;
-
-    a {
-      margin: 0 auto;
-    }
-
-    img {
-      max-width: 33.3vw;
-      max-height: 33.3vw;
-      border: none !important;
-    }
-  }
-
-  .user-disable-cropped-false {
-    article.post-preview {
-      width: 33.3%;
-      height: 33.3vw;
-      overflow: hidden;
-    }
-
-    img {
-      width: 33.3vw;
-      height: 33.3vw;
-
-      &.has-cropped-false {
-        object-fit: cover;
-      }
-    }
+    width: 154px;
+    margin: 0 10px 10px 0;
+    vertical-align: top;
+  }
+}
+
+@media screen and (max-width: 660px) {
+  article.post-preview img {
+    border: none !important;
   }
 }