feat(timeline-editor): Add time indicator, sequence flash, and taller view

Visual Enhancements:

1. Current Time Indicator (Vertical Line)
   - Faint vertical line shows current scroll position
   - Fixed position at left: 80px with gradient fade
   - Color: rgba(78, 201, 176, 0.6) (teal/cyan)
   - Gradient: fades at top/bottom for smooth appearance
   - pointer-events: none (doesn't block interaction)
   - z-index: 100 (appears above timeline elements)
   - Guides the eye during mouse wheel navigation

2. Sequence Flash Effect
   - Brief highlight when active sequence changes
   - 0.6s animation: bright glow → normal state
   - Keyframe animation sequenceFlash:
     * Start: box-shadow 20px glow, teal border
     * End: normal 10px glow, blue border
   - Triggers on lastActiveSeqIndex change
   - Auto-removes class after 600ms
   - Helps user track which sequence is now active

3. Taller Timeline View
   - timeline-container: height = calc(100vh - 280px)
   - min-height: 500px (prevents over-shrinking)
   - Uses full vertical real estate
   - Much less squished appearance
   - Better utilization of screen space
   - Accommodates more sequences in viewport

Technical Implementation:
- Added lastActiveSeqIndex global state variable
- Wheel handler detects sequence index changes
- querySelector to find sequence div and add flash class
- setTimeout removes flash class after animation
- Fixed positioning for time indicator
- Responsive height calculation for container

User Experience:
- Visual feedback during diagonal scrolling
- Clear indication of current time position
- Smooth flash draws attention to sequence changes
- More comfortable editing with taller view
- Better spatial awareness of timeline position

1 files changed, 53 insertions, 1 deletions

diff --git a/tools/timeline_editor/index.html b/tools/timeline_editor/index.html
index ea8b454..ffaf74f 100644
--- a/tools/timeline_editor/index.html
+++ b/tools/timeline_editor/index.html
@@ -102,14 +102,34 @@
             border-radius: 8px;
             padding: 20px;
             overflow-x: auto;
+            overflow-y: auto;
+            position: relative;
+            height: calc(100vh - 280px);
+            min-height: 500px;
         }
 
         .timeline {
             position: relative;
-            min-height: 400px;
+            min-height: 100%;
             border-left: 2px solid #3c3c3c;
         }
 
+        .current-time-indicator {
+            position: fixed;
+            left: 80px;
+            top: 0;
+            bottom: 0;
+            width: 2px;
+            background: linear-gradient(to bottom,
+                rgba(78, 201, 176, 0) 0%,
+                rgba(78, 201, 176, 0.6) 10%,
+                rgba(78, 201, 176, 0.6) 90%,
+                rgba(78, 201, 176, 0) 100%);
+            pointer-events: none;
+            z-index: 100;
+            opacity: 0.7;
+        }
+
         .time-markers {
             position: relative;
             height: 30px;
@@ -154,6 +174,21 @@
             box-shadow: 0 0 10px rgba(78, 201, 176, 0.5);
         }
 
+        .sequence.active-flash {
+            animation: sequenceFlash 0.6s ease-out;
+        }
+
+        @keyframes sequenceFlash {
+            0% {
+                box-shadow: 0 0 20px rgba(78, 201, 176, 0.8);
+                border-color: #4ec9b0;
+            }
+            100% {
+                box-shadow: 0 0 10px rgba(14, 99, 156, 0.5);
+                border-color: #0e639c;
+            }
+        }
+
         .sequence-name {
             position: absolute;
             top: 50%;
@@ -370,6 +405,7 @@
         <div class="timeline-container">
             <div class="time-markers" id="timeMarkers"></div>
             <div class="timeline" id="timeline"></div>
+            <div class="current-time-indicator" id="timeIndicator"></div>
         </div>
 
         <button class="panel-collapse-btn" id="panelCollapseBtn">◀ Properties</button>
@@ -395,6 +431,7 @@
         let bpm = 120;
         let isDragging = false;
         let dragOffset = { x: 0, y: 0 };
+        let lastActiveSeqIndex = -1;
 
         // DOM elements
         const timeline = document.getElementById('timeline');
@@ -951,6 +988,21 @@
                 }
             }
 
+            // Flash effect when active sequence changes
+            if (targetSeqIndex !== lastActiveSeqIndex && sequences.length > 0) {
+                lastActiveSeqIndex = targetSeqIndex;
+
+                // Add flash class to target sequence
+                const seqDivs = timeline.querySelectorAll('.sequence');
+                if (seqDivs[targetSeqIndex]) {
+                    seqDivs[targetSeqIndex].classList.add('active-flash');
+                    // Remove class after animation completes
+                    setTimeout(() => {
+                        seqDivs[targetSeqIndex]?.classList.remove('active-flash');
+                    }, 600);
+                }
+            }
+
             // Smooth vertical scroll to bring target sequence to top of viewport
             const targetScrollTop = targetSeqIndex * 80; // 80px per sequence
             const currentScrollTop = timelineContainer.scrollTop;