feat: wire sidebar toggle button click handlers

frontend/app.js

@@ -960,6 +960,8 @@ function updateSessionPill(sessions) {
  */
 function bindStaticEventListeners() {
   on($('back-btn'), 'click', closeSession);
+  on($('sidebar-toggle-btn'), 'click', toggleSidebar);
+  on($('sidebar-collapse-btn'), 'click', toggleSidebar);
   on($('palette-trigger'), 'click', openPalette);
   on($('palette-backdrop'), 'click', closePalette);
   document.addEventListener('keydown', handleGlobalKeydown);

frontend/tests/test_app.mjs

@@ -1926,3 +1926,30 @@ test('toggleSidebar removes sidebar--collapsed class when opening (from closed)
 
   globalThis.document.getElementById = origGetById;
 });
+
+// --- bindStaticEventListeners sidebar toggle buttons ---
+
+test('bindStaticEventListeners binds sidebar-toggle-btn and sidebar-collapse-btn click to toggleSidebar', () => {
+  const eventsBound = {};
+  const origGetById = globalThis.document.getElementById;
+  const origDocAddListener = globalThis.document.addEventListener;
+  globalThis.document.getElementById = (id) => {
+    const el = { _events: {}, addEventListener: (ev, fn) => { el._events[ev] = fn; } };
+    eventsBound[id] = el;
+    return el;
+  };
+  globalThis.document.addEventListener = () => {};
+
+  app.bindStaticEventListeners();
+
+  assert.ok(
+    eventsBound['sidebar-toggle-btn'] && 'click' in eventsBound['sidebar-toggle-btn']._events,
+    '#sidebar-toggle-btn should have a click listener',
+  );
+  assert.ok(
+    eventsBound['sidebar-collapse-btn'] && 'click' in eventsBound['sidebar-collapse-btn']._events,
+    '#sidebar-collapse-btn should have a click listener',
+  );
+  globalThis.document.getElementById = origGetById;
+  globalThis.document.addEventListener = origDocAddListener;
+});