Add Unsorted folder auto-sort with keyword matching

Scans an Unsorted folder at the library root and proposes destinations
for new courses by matching keywords against the existing category
tree, suggesting new subfolders when nothing matches closely, and
flagging items for manual review when nothing matches at all. Review
and apply happen on a dedicated /unsorted page linked from Settings;
nothing moves until the user confirms.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/settings.html

@@ -462,6 +462,16 @@
             </div>
         </div>
 
+        <div class="card">
+            <h2>Sort Unsorted Courses</h2>
+            <p class="setting-desc" style="margin-bottom: 12px;">
+                Drop new courses in an "Unsorted" folder at the root of your library, then use this to
+                propose where each one belongs based on your existing folder structure - nothing moves
+                until you review and confirm on its own page.
+            </p>
+            <a class="btn btn-secondary" href="/unsorted">{{ icons.icon('folder', 14) }} Open Sorter</a>
+        </div>
+
         <div class="card">
             <h2>Manage Library</h2>
             <p class="setting-desc" style="margin-bottom: 12px;">