feat(02-03): build transport UI and waveform canvas

- Replace timeline placeholder with waveform canvas + playback cursor
- Replace transport placeholder with full transport bar controls
- Add play/pause/stop buttons, seek slider, time display, audio path input
- Add drawWaveform(), loadWaveform(), updatePosition(), formatTime() to app.js
- Dispatch msg.type=tick to updatePosition in handleMessage
- Wire transport buttons via WebSocket commands
- Add transport/waveform styles to style.css using existing CSS variables
- Deploy via ~/bin/deploy.sh

lightsync/frontend/style.css

@@ -247,3 +247,93 @@ button:hover {
     color: #ff3333;
     border: none;
 }
+
+/* Transport controls */
+.transport-controls {
+    display: flex;
+    gap: 4px;
+    align-items: center;
+}
+
+.transport-btn {
+    background: var(--bg-panel);
+    color: var(--accent);
+    border: 1px solid var(--border-dim);
+    padding: 4px 10px;
+    font-family: var(--font-mono);
+    font-size: 0.85rem;
+    cursor: pointer;
+    min-width: 36px;
+    text-align: center;
+}
+
+.transport-btn:hover {
+    background: var(--accent);
+    color: var(--bg-primary);
+    border-color: var(--accent);
+}
+
+.transport-time {
+    font-family: var(--font-mono);
+    font-size: 0.85rem;
+    white-space: nowrap;
+    min-width: 120px;
+}
+
+.transport-seek {
+    flex: 1;
+    display: flex;
+    align-items: center;
+}
+
+.seek-slider {
+    width: 100%;
+    accent-color: var(--accent);
+    cursor: pointer;
+}
+
+.transport-file {
+    display: flex;
+    gap: 4px;
+    align-items: center;
+}
+
+.audio-path-input {
+    background: var(--bg-primary);
+    color: var(--text-primary);
+    border: 1px solid var(--border-dim);
+    padding: 4px 8px;
+    font-family: var(--font-mono);
+    font-size: 0.8rem;
+    width: 200px;
+}
+
+.audio-path-input:focus {
+    border-color: var(--accent);
+    outline: none;
+}
+
+/* Transport bar layout override */
+.transport-bar {
+    gap: 12px;
+    padding: 6px 12px;
+}
+
+/* Waveform */
+.waveform-container {
+    background: var(--bg-primary);
+    border: none;
+    overflow: hidden;
+}
+
+.playback-cursor {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 2px;
+    height: 100%;
+    background: var(--accent);
+    pointer-events: none;
+    transition: left 0.1s linear;
+    z-index: 10;
+}