Timeline editor: fix waveform click position calculation

Read actual canvas offset from style.left instead of assuming scrollLeft.
Canvas is positioned with negative left offset, so we subtract it to get
correct beat position.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/tools/timeline_editor/index.html b/tools/timeline_editor/index.html
index 402c580..4ea93f2 100644
--- a/tools/timeline_editor/index.html
+++ b/tools/timeline_editor/index.html
@@ -851,7 +851,8 @@
         dom.waveformContainer.addEventListener('click', async e => {
             if (!state.audioBuffer) return;
             const rect = dom.waveformContainer.getBoundingClientRect();
-            const clickX = e.clientX - rect.left + dom.timelineContent.scrollLeft;
+            const canvasOffset = parseFloat(dom.waveformCanvas.style.left) || 0;
+            const clickX = e.clientX - rect.left - canvasOffset;
             const clickBeats = clickX / state.pixelsPerSecond;
             const clickTime = beatsToTime(clickBeats);
             const wasPlaying = state.isPlaying;