FEATURE: add HTML replacements

This adds support for Watched Words to allow replacement with HTML content rather than always replacing with text.

Can be useful when automatically replacing with the '<abbr>' tag for example.

Discussion - https://meta.discourse.org/t/replace-text-with-more-than-just-links/305672

db/migrate/20240506125839_add_html_to_watched_words.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddHtmlToWatchedWords < ActiveRecord::Migration[7.0]
+  def change
+    add_column :watched_words, :html, :boolean, default: false, null: false
+  end
+end