add inventory sort control to the ui

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

trade-hub/frontend/src/index.html

@@ -68,6 +68,12 @@
         <option value="ship-items">Ship Equipment</option>
         <option value="fps-items">FPS Items</option>
       </select>
+      <select id="inv-sort" aria-label="Sort inventory">
+        <option value="name">Sort: Name</option>
+        <option value="category">Sort: Category</option>
+        <option value="quantity">Sort: Quantity</option>
+        <option value="updated">Sort: Recently updated</option>
+      </select>
     </div>
     <div id="inv-summary" class="inv-summary"></div>
     <div id="inv-empty" class="empty-state hidden">