fix: uncollapse button ☰ appears when sidebar is hidden

When sidebarCollapsed=true, a hamburger button appears at top-left
corner to restore the sidebar. CSS fixed positioning outside sidebar
so it's always visible even when sidebar is collapsed.

app/templates/base.html

@@ -268,6 +268,11 @@
     </div>
   </aside>
 
+  <!-- Uncollapse button (visible when sidebar hidden) -->
+  <button class="sidebar-uncollapse-btn" x-show="sidebarCollapsed" @click="sidebarCollapsed = false" title="Show sidebar">
+    <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="3" y1="6" x2="21" y2="6"/><line x1="3" y1="12" x2="21" y2="12"/><line x1="3" y1="18" x2="21" y2="18"/></svg>
+  </button>
+
   <!-- ═══════════ MAIN ═══════════ -->
   <div class="main-wrapper">
 

static/css/app.css

@@ -2499,3 +2499,12 @@ input, select, textarea { font-family: inherit; color: inherit; }
   .get-started-toolbar { flex-wrap: wrap; justify-content: center; }
   .gs-pill { font-size: 12px; padding: 6px 12px; }
 }
+
+/* ══════════ Uncollapse sidebar button ══════════ */
+.sidebar-uncollapse-btn {
+  position: fixed; top: 12px; left: 12px; z-index: 1001;
+  width: 36px; height: 36px; display: flex; align-items: center; justify-content: center;
+  background: var(--bg-secondary); border: 1px solid var(--border);
+  border-radius: 8px; color: var(--text-secondary); cursor: pointer;
+}
+.sidebar-uncollapse-btn:hover { background: var(--bg-hover); color: var(--text); }