feat(04-01): TimelineCanvas class + CSS + app.js wiring

- Create lightsync/frontend/timeline/timeline.js with TimelineCanvas class
  - Per-device horizontal tracks with track headers and time axis
  - HiDPI canvas rendering with devicePixelRatio handling
  - Waveform peaks background layer, beat marks overlay, cue block rendering
  - Playback cursor synced to audio.currentTime via requestAnimationFrame
  - Auto-scroll when cursor approaches right edge
  - Mouse wheel scrolling on timeline canvas
  - loadTracks(), loadWaveform(), loadBeats() data loading methods
  - Empty state messages when no devices or audio loaded
- Add timeline CSS to style.css (toolbar, canvas, inspector strip, snap button)
- Wire timeline into app.js: import, initTimeline(), zoom/beat-offset/snap controls
- Remove old animation-grid click listener (element no longer exists in main-area)
- Populate animation palette dynamically in sidebar with 7 animation types

lightsync/frontend/style.css

@@ -354,3 +354,133 @@ button:hover {
 
 .text-dim    { color: var(--text-dim); }
 .text-accent { color: var(--text-accent); }
+
+/* ── Timeline ──────────────────────────────────── */
+#timeline-canvas {
+    flex: 1;
+    display: block;
+    min-height: 0;
+    cursor: default;
+}
+
+.timeline-toolbar {
+    height: 32px;
+    background: var(--bg-panel-dark);
+    border-bottom: 1px solid var(--border-dim);
+    display: flex;
+    align-items: center;
+    gap: 16px;
+    padding: 0 12px;
+    flex-shrink: 0;
+}
+
+.toolbar-field {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+}
+
+.toolbar-label {
+    font-size: 10px;
+    text-transform: uppercase;
+    color: var(--text-dim);
+    letter-spacing: 0.1em;
+    white-space: nowrap;
+}
+
+.toolbar-unit {
+    font-size: 10px;
+    color: var(--text-dim);
+}
+
+.toolbar-sep {
+    width: 1px;
+    height: 20px;
+    background: var(--border-dim);
+    flex-shrink: 0;
+}
+
+#zoom-slider {
+    width: 100px;
+    accent-color: var(--accent);
+    height: 3px;
+}
+
+#beat-offset {
+    width: 70px;
+    font-size: 12px;
+    padding: 2px 4px;
+}
+
+.snap-btn.active {
+    background: var(--accent);
+    color: var(--bg-primary);
+    border-color: var(--accent);
+}
+
+/* ── Block Inspector Strip ─────────────────────── */
+.block-inspector {
+    height: 40px;
+    background: var(--bg-panel-dark);
+    border-top: 1px solid var(--border-dim);
+    display: flex;
+    align-items: center;
+    gap: 16px;
+    padding: 0 12px;
+    flex-shrink: 0;
+}
+
+.inspector-label {
+    color: var(--text-accent);
+    font-size: 14px;
+    font-weight: 600;
+    text-transform: uppercase;
+    flex-shrink: 0;
+    min-width: 120px;
+}
+
+.inspector-field {
+    display: flex;
+    align-items: center;
+    gap: 4px;
+    font-size: 10px;
+    text-transform: uppercase;
+    color: var(--text-dim);
+    letter-spacing: 0.1em;
+}
+
+.inspector-field input,
+.inspector-field select {
+    font-size: 12px;
+    padding: 2px 4px;
+    background: var(--bg-panel);
+    border: 1px solid var(--border-dim);
+    color: var(--text-primary);
+    font-family: var(--font-mono);
+}
+
+.inspector-field input[type="number"] {
+    width: 60px;
+}
+
+.inspector-color-swatch {
+    width: 16px;
+    height: 16px;
+    border: 1px solid var(--border-dim);
+    cursor: pointer;
+    flex-shrink: 0;
+}
+
+.inspector-remove {
+    margin-left: auto;
+    background: none;
+    border: none;
+    color: var(--text-dim);
+    font-size: 16px;
+    cursor: pointer;
+    padding: 0 4px;
+}
+.inspector-remove:hover {
+    color: #ff3333;
+    border: none;
+}