fix: Ctrl+S saves section in SECTION-TAB, Ctrl+A selects all items

Ctrl+S in SECTION-TAB (activeTab starts with session_):
calls handleSaveSectionTab(curTab).
Ctrl+A in MAIN/SECTION-TAB: collects sections, midiItems,
clips from activeTracksRef.current into selectedItemIds.
Ignores sub-tab contexts (PIANO_ROLL).

app/static/js/app.jsx

@@ -8050,6 +8050,19 @@ const App = () => {
         showToast('New project created', 'info');
         return;
       }
+      if (ctrl && !alt && !e.shiftKey && e.key === 'a') {
+        e.preventDefault();
+        const curTab = activeTabRef.current;
+        if (curTab !== 'main' && !curTab.startsWith('session_')) return;
+        const allIds = new Set();
+        (activeTracksRef.current || []).forEach(t => {
+          (t.sections || []).forEach(s => allIds.add(s.id));
+          (t.midiItems || []).forEach(m => allIds.add(m.id));
+          (t.clips || []).forEach(c => allIds.add(c.id === 'default' ? 'default_' + t.id : c.id));
+        });
+        setSelectedItemIds(allIds);
+        return;
+      }
       if (ctrl && !alt && e.key === 's') {
         e.preventDefault();
         handleExportSFS();
@@ -8155,6 +8168,10 @@ const App = () => {
             }
             showToast('Đã lưu', 'success');
           });
+        } else if (curTab.startsWith('session_')) {
+          // Section tab: save section
+          handleSaveSectionTab(curTab);
+          showToast('Đã lưu Section', 'success');
         } else {
           // Sub-tab: save current tab
           const st = subTabsRef.current.find(s => s.id === curTab);