feat(ui): remove '+ Type' button from sidebar legend

Cable type creation is managed via the admin modal (⚙ → Cable types
tab), which makes the prominent sidebar affordance unnecessary. Drop
the button element and its click handler; the legend itself (rows,
edit button per row, active-type selection) is unchanged.

web/static/index.html

@@ -36,7 +36,6 @@
       <section class="legend">
         <h2 class="sidebar-heading">Cable types</h2>
         <ul id="legend-list" class="legend-list"></ul>
-        <button type="button" id="btn-add-type" class="btn btn-tiny">+ Type</button>
       </section>
       <section class="tools">
         <h2 class="sidebar-heading">Tools</h2>

web/static/main.js

@@ -3224,7 +3224,6 @@ async function boot() {
   bindCloseButtons($("#modal-admin"));
 
   $("#btn-new-project").addEventListener("click", openNewProjectModal);
-  $("#btn-add-type").addEventListener("click", () => openCableTypeModal(null));
   $("#btn-delete-project").addEventListener("click", openDeleteProjectModal);
   $("#btn-admin").addEventListener("click", openAdminModal);
   $("#btn-solve").addEventListener("click", openSolveModal);