fix: Transport lifecycle, scope zoom, clear button, and freq routing

- Fix pianoroll/sequencer Transport not resetting on stop/restart (notes
  were scheduled in the past and never fired)
- Stop and cancel Transport in stopAudio() to prevent stale events
- Add zoom +/- buttons to scope widget (6 levels, 64–2048 samples)
- Increase scope analyser buffer from 256 to 2048 for wider time view
- Add vertical grid lines to scope display
- Add "Limpiar" clear canvas button to PuzzleView
- Skip audio-graph connection for keyboard/seq/pianoroll freq→osc freq
  (direct frequency setting prevents inaudible ultrasonic values)
- Auto-trigger envelopes without gate connections for noise/ambient levels

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/PianoRollWidget.jsx

@@ -235,12 +235,23 @@ export default function PianoRollWidget({ moduleId }) {
   // Playback
   useEffect(() => {
     if (!state.isRunning) {
-      if (partRef.current) { partRef.current.stop(); partRef.current.dispose(); partRef.current = null; }
+      if (partRef.current) {
+        try { partRef.current.stop(); } catch {}
+        try { partRef.current.dispose(); } catch {}
+        partRef.current = null;
+      }
       setPlayPos(-1);
       return;
     }
 
-    Tone.getTransport().bpm.value = bpm;
+    const transport = Tone.getTransport();
+    transport.bpm.value = bpm;
+
+    // Ensure Transport is at position 0 before scheduling
+    if (transport.state === 'started') {
+      transport.stop();
+    }
+    transport.position = 0;
 
     // Build Tone.Part from notes using musical time (bars:quarters:sixteenths)
     // This lets the Transport BPM control actual playback speed
@@ -263,7 +274,7 @@ export default function PianoRollWidget({ moduleId }) {
       // Note-off: convert duration beats to musical time for proper BPM-relative timing
       const durSixteenths = Math.round(ev.dur * 4);
       const noteOffTime = time + (durSixteenths * (60 / (bpm * 4))) * 0.9;
-      Tone.getTransport().scheduleOnce(() => {
+      transport.scheduleOnce(() => {
         setSequencerSignals(moduleId, midiToFreq(ev.note), false);
       }, noteOffTime);
     }, events.map(ev => [ev.time, { note: ev.note, dur: ev.dur }]));
@@ -271,16 +282,15 @@ export default function PianoRollWidget({ moduleId }) {
     part.loop = loop;
     part.loopEnd = `${bars}m`;
     part.start(0);
-
-    if (Tone.getTransport().state !== 'started') {
-      Tone.getTransport().start();
-    }
     partRef.current = part;
 
+    // Start Transport fresh from position 0
+    transport.start();
+
     // Track playhead position
     const posInterval = setInterval(() => {
-      if (Tone.getTransport().state === 'started') {
-        const pos = Tone.getTransport().seconds;
+      if (transport.state === 'started') {
+        const pos = transport.seconds;
         const beatDuration = 60 / bpm;
         const currentBeat = (pos / beatDuration) % totalBeats;
         setPlayPos(currentBeat);
@@ -289,7 +299,11 @@ export default function PianoRollWidget({ moduleId }) {
 
     return () => {
       clearInterval(posInterval);
-      if (partRef.current) { partRef.current.stop(); partRef.current.dispose(); partRef.current = null; }
+      if (partRef.current) {
+        try { partRef.current.stop(); } catch {}
+        try { partRef.current.dispose(); } catch {}
+        partRef.current = null;
+      }
     };
   }, [state.isRunning, moduleId, bpm, bars, loop]);