Retire vendored cacycle_diff.js for a diff-lcs-based diff view

Revisions#diff now computes an inline or side-by-side word diff
server-side (Page#diff_against, lib/html_word_diff.rb) instead of
shipping raw/escaped content to the browser for a 2008-era vendored
JS differ to mangle. View mode is picked via a `view` param, settable
either on the diff page itself or directly from the revisions#index
sticky bar next to "Diff revisions".

Also fixes a pre-existing bug in RevisionsController#diff's single-
revision branch, which set params[:start]/params[:end] instead of
params[:start_revision]/params[:end_revision].

1 files changed, 25 insertions, 0 deletions

diff --git a/public/stylesheets/admin.css b/public/stylesheets/admin.css
index 38c9e5a..1bb6cf4 100644
--- a/public/stylesheets/admin.css
+++ b/public/stylesheets/admin.css
@@ -511,6 +511,31 @@ table.revisions_table tr:hover {
   background-color: #f1f1f1;
 }
 
+#diffview del {
+  background: #ffd7d5;
+  color: #82071e;
+  text-decoration: line-through;
+  padding: 0 2px;
+  border-radius: 2px;
+}
+
+#diffview ins {
+  background: #ccffd8;
+  color: #055d20;
+  text-decoration: none;
+  padding: 0 2px;
+  border-radius: 2px;
+}
+
+#diffview .diff_side_by_side {
+  display: flex;
+  gap: 1rem;
+}
+
+#diffview .diff_column {
+  flex: 1;
+}
+
 table.user_table td.user_login {
   padding-right: 30px;
 }