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>