fix(piano-roll): seek-to-start restarts playback

- Add seekPlaybackTo(time) that stops, updates refs, reschedules
  MIDI, and restarts playback for both sub-tab and main timeline
- 'Quay lại đầu' and 'Đầu vùng chọn' buttons use seekPlaybackTo

app/static/js/app.jsx

@@ -10118,6 +10118,46 @@ const App = () => {
       isPlaying: false
     })));
   };
+  const seekPlaybackTo = (time) => {
+    const isSubTab = subTabs.some(sub => sub.id === activeTab);
+    if (isSubTab) {
+      const st = subTabs.find(s => s.id === activeTab);
+      if (!st) return;
+      if (st.isPlaying) {
+        stopAllPlayback();
+        window.SonicSF.stopAll();
+        setSubTabs(prev => prev.map(s => s.id === activeTab ? {
+          ...s,
+          currentTime: time,
+          isPlaying: true
+        } : s));
+        const ctx = getAudioContext();
+        startOffsetTimeRef.current = time;
+        startAudioTimeRef.current = ctx.currentTime;
+        startBufferOffsetRef.current = time * (st.speed || 1.0);
+        if (st.type === 'PIANO_ROLL') {
+          schedulePianoRollMidi(st, time);
+        }
+        startSubTabPlayback(st, time);
+      } else {
+        setSubTabs(prev => prev.map(s => s.id === activeTab ? {
+          ...s,
+          currentTime: time
+        } : s));
+      }
+    } else {
+      if (isPlaying) {
+        stopAllPlayback();
+        setCurrentTime(time);
+        startOffsetTimeRef.current = time;
+        startAudioTimeRef.current = getAudioContext().currentTime;
+        startTrackPlayback(time);
+        setIsPlaying(true);
+      } else {
+        setCurrentTime(time);
+      }
+    }
+  };
   const handleStop = () => {
     if (recordingStateRef.current === 'RECORDING' || recordingStateRef.current === 'COUNT_IN') {
       stopRecordingTake();
@@ -14488,17 +14528,7 @@ const App = () => {
   })))), /*#__PURE__*/React.createElement("div", {
     className: "w-[1px] h-5 bg-zinc-800 mx-0.5"
   }), /*#__PURE__*/React.createElement("button", {
-    onClick: () => {
-      const isSubTab = subTabs.some(sub => sub.id === activeTab);
-      if (isSubTab) {
-        setSubTabs(prev => prev.map(s => s.id === activeTab ? {
-          ...s,
-          currentTime: 0
-        } : s));
-      } else {
-        setCurrentTime(0);
-      }
-    },
+    onClick: () => seekPlaybackTo(0),
     className: "w-7 h-7 flex items-center justify-center bg-zinc-800 hover:bg-zinc-700 text-zinc-200 rounded border border-zinc-700 transition",
     title: "Quay lại đầu"
   }, /*#__PURE__*/React.createElement("span", {
@@ -14510,16 +14540,12 @@ const App = () => {
     onClick: () => {
       const isSubTab = subTabs.some(sub => sub.id === activeTab);
       if (isSubTab) {
-        setSubTabs(prev => prev.map(s => {
-          if (s.id !== activeTab) return s;
-          const left = s.selectionStart !== null && s.selectionEnd !== null ? Math.min(s.selectionStart, s.selectionEnd) : null;
-          return left !== null ? {
-            ...s,
-            currentTime: left
-          } : s;
-        }));
+        const st = subTabs.find(s => s.id === activeTab);
+        if (!st) return;
+        const left = st.selectionStart !== null && st.selectionEnd !== null ? Math.min(st.selectionStart, st.selectionEnd) : null;
+        if (left !== null) seekPlaybackTo(left);
       } else {
-        if (selLeft !== null) setCurrentTime(selLeft);
+        if (selLeft !== null) seekPlaybackTo(selLeft);
       }
     },
     className: "w-7 h-7 flex items-center justify-center bg-zinc-800 hover:bg-zinc-700 text-zinc-200 rounded border border-zinc-700 transition",