fix(timeline-editor): Dynamic sequence bounds, mouse wheel scroll, responsive layout

Bug Fix #1: Dynamic Sequence Start Time
- Sequences now dynamically adjust start position based on earliest effect
- Sequence box shrinks from left when effects move later in time
- Calculate visual bounds: min(effect.startTime) to max(effect.endTime)
- Sequence position: seq.startTime + minEffectStart
- Sequence width: maxEffectEnd - minEffectStart
- Time display shows actual visual start time, not fixed seq.startTime
- Eliminates empty space at sequence start when effects are delayed

Bug Fix #2: Mouse Wheel Horizontal Scroll
- Mouse wheel now scrolls timeline horizontally (natural navigation)
- Prevents default vertical scroll behavior on timeline container
- More intuitive than using horizontal scrollbar
- Smooth scrolling with deltaY mapped to scrollLeft

Bug Fix #3: Responsive Layout
- Container now uses 100% width (was: fixed 1400px max)
- Added window resize event listener to re-render timeline
- Body uses box-sizing: border-box for proper padding
- Timeline recalculates on browser window resize
- Works correctly when going fullscreen

Technical details:
- seqVisualStart = seq.startTime + Math.min(effect.startTime)
- seqVisualEnd = seq.startTime + Math.max(effect.endTime)
- Wheel event uses { passive: false } to allow preventDefault()
- Window resize debouncing not needed (renderTimeline is fast)

1 files changed, 33 insertions, 9 deletions

diff --git a/tools/timeline_editor/index.html b/tools/timeline_editor/index.html
index 4dd37ee..22e5239 100644
--- a/tools/timeline_editor/index.html
+++ b/tools/timeline_editor/index.html
@@ -16,11 +16,16 @@
             background: #1e1e1e;
             color: #d4d4d4;
             padding: 20px;
+            margin: 0;
+            min-height: 100vh;
+            box-sizing: border-box;
         }
 
         .container {
-            max-width: 1400px;
+            max-width: 100%;
+            width: 100%;
             margin: 0 auto;
+            box-sizing: border-box;
         }
 
         header {
@@ -393,6 +398,7 @@
 
         // DOM elements
         const timeline = document.getElementById('timeline');
+        const timelineContainer = document.querySelector('.timeline-container');
         const fileInput = document.getElementById('fileInput');
         const saveBtn = document.getElementById('saveBtn');
         const addSequenceBtn = document.getElementById('addSequenceBtn');
@@ -573,30 +579,37 @@
                 seqDiv.className = 'sequence';
                 seqDiv.dataset.index = seqIndex;
 
-                // Calculate sequence duration based on effects
-                let seqDuration = 10; // Default
+                // Calculate sequence bounds based on effects (dynamic start/end)
+                let seqVisualStart = seq.startTime;
+                let seqVisualEnd = seq.startTime + 10; // Default 10s duration
+
                 if (seq.effects.length > 0) {
-                    seqDuration = Math.max(...seq.effects.map(e => e.endTime));
+                    const minEffectStart = Math.min(...seq.effects.map(e => e.startTime));
+                    const maxEffectEnd = Math.max(...seq.effects.map(e => e.endTime));
+                    seqVisualStart = seq.startTime + minEffectStart;
+                    seqVisualEnd = seq.startTime + maxEffectEnd;
                 }
 
+                const seqVisualWidth = seqVisualEnd - seqVisualStart;
+
                 // Calculate sequence height based on number of effects (stacked vertically)
                 const numEffects = seq.effects.length;
                 const effectSpacing = 30; // Reduced from 40px
                 const seqHeight = Math.max(70, 20 + numEffects * effectSpacing + 5);
 
-                seqDiv.style.left = `${seq.startTime * pixelsPerSecond}px`;
+                seqDiv.style.left = `${seqVisualStart * pixelsPerSecond}px`;
                 seqDiv.style.top = `${seqIndex * 80}px`;
-                seqDiv.style.width = `${seqDuration * pixelsPerSecond}px`;
+                seqDiv.style.width = `${seqVisualWidth * pixelsPerSecond}px`;
                 seqDiv.style.height = `${seqHeight}px`;
 
-                // Format time display based on mode
+                // Format time display based on mode (show visual start, not seq.startTime)
                 let seqTimeDisplay;
                 if (showBeats) {
                     const beatDuration = 60.0 / bpm;
-                    const startBeat = (seq.startTime / beatDuration).toFixed(1);
+                    const startBeat = (seqVisualStart / beatDuration).toFixed(1);
                     seqTimeDisplay = `Start: ${startBeat}b`;
                 } else {
-                    seqTimeDisplay = `Start: ${seq.startTime.toFixed(2)}s`;
+                    seqTimeDisplay = `Start: ${seqVisualStart.toFixed(2)}s`;
                 }
 
                 // Create sequence name overlay (large, centered, fades on hover)
@@ -916,6 +929,17 @@
             updateProperties();
         });
 
+        // Mouse wheel horizontal scroll
+        timelineContainer.addEventListener('wheel', (e) => {
+            e.preventDefault();
+            timelineContainer.scrollLeft += e.deltaY;
+        }, { passive: false });
+
+        // Window resize handler
+        window.addEventListener('resize', () => {
+            renderTimeline();
+        });
+
         // Utilities
         function showMessage(text, type) {
             messageArea.innerHTML = `<div class="${type}">${text}</div>`;