Add hidden setting to puzzles

#19

app/views/puzzles/index.html.slim

@@ -16,6 +16,8 @@
             = t("activerecord.attributes.puzzle.brand")
           th
             = t("activerecord.attributes.puzzle.pieces")
+          th
+            = t("activerecord.attributes.puzzle.hidden")
       tbody
         - @puzzles.each do |puzzle|
           tr.align-middle scope="row"
@@ -27,6 +29,12 @@
               = puzzle.brand
             td
               = puzzle.pieces
+            td
+              - if puzzle.hidden?
+                <svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-check-square" viewBox="0 0 16 16">
+                  <path d="M14 1a1 1 0 0 1 1 1v12a1 1 0 0 1-1 1H2a1 1 0 0 1-1-1V2a1 1 0 0 1 1-1zM2 0a2 2 0 0 0-2 2v12a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V2a2 2 0 0 0-2-2z"/>
+                  <path d="M10.97 4.97a.75.75 0 0 1 1.071 1.05l-3.992 4.99a.75.75 0 0 1-1.08.02L4.324 8.384a.75.75 0 1 1 1.06-1.06l2.094 2.093 3.473-4.425z"/>
+                </svg>
             td
               a.btn.btn-sm.btn-secondary href=edit_contest_puzzle_path(@contest, puzzle)
                 = t("helpers.buttons.edit")