feat: Replaced thin 3px line markers with 12px color-coded circle pins,…

- "frontend/src/components/ChapterMarkers.tsx"
- "frontend/src/components/PlayerControls.tsx"
- "frontend/src/App.css"

GSD-Task: S02/T01

frontend/src/App.css

@@ -29,6 +29,12 @@
   --color-accent-subtle: rgba(34, 211, 238, 0.1);
   --color-accent-focus: rgba(34, 211, 238, 0.15);
 
+  /* Content-type pin colors */
+  --color-pin-technique: #22d3ee;   /* cyan */
+  --color-pin-settings: #f59e0b;    /* amber */
+  --color-pin-reasoning: #a855f7;   /* purple */
+  --color-pin-workflow: #22c55e;    /* green */
+
   /* Shadows / overlays */
   --color-shadow: rgba(0, 0, 0, 0.2);
   --color-shadow-heavy: rgba(0, 0, 0, 0.4);
@@ -6238,42 +6244,69 @@ a.app-footer__about:hover,
   pointer-events: none;
 }
 
-.chapter-marker__tick {
+.chapter-marker__pin {
   position: absolute;
-  width: 3px;
-  height: 100%;
+  width: 12px;
+  height: 12px;
+  border-radius: 50%;
   background: var(--color-accent, #22d3ee);
-  opacity: 0.6;
+  opacity: 0.7;
   pointer-events: all;
   cursor: pointer;
-  transform: translateX(-50%);
-  border: none;
+  transform: translate(-50%, -50%);
+  top: 50%;
+  border: 2px solid rgba(0, 0, 0, 0.4);
   padding: 0;
   font: inherit;
+  transition: transform 150ms ease, opacity 150ms ease;
+  /* Ensure touch-friendly hit area */
+  min-width: 12px;
+  min-height: 12px;
 }
 
-.chapter-marker__tick:hover {
+.chapter-marker__pin::before {
+  content: "";
+  position: absolute;
+  inset: -6px;
+}
+
+.chapter-marker__pin--technique { background: var(--color-pin-technique); }
+.chapter-marker__pin--settings  { background: var(--color-pin-settings); }
+.chapter-marker__pin--reasoning { background: var(--color-pin-reasoning); }
+.chapter-marker__pin--workflow  { background: var(--color-pin-workflow); }
+
+.chapter-marker__pin--active {
   opacity: 1;
+  transform: translate(-50%, -50%) scale(1.3);
+  z-index: 2;
+}
+
+.chapter-marker__pin:hover {
+  opacity: 1;
+  transform: translate(-50%, -50%) scale(1.2);
+}
+
+.chapter-marker__pin--active:hover {
+  transform: translate(-50%, -50%) scale(1.3);
 }
 
 .chapter-marker__tooltip {
   position: absolute;
-  bottom: 100%;
+  bottom: calc(100% + 4px);
   left: 50%;
   transform: translateX(-50%);
   background: var(--color-bg-surface, #1e293b);
   color: var(--text-primary, #e2e8f0);
-  padding: 4px 8px;
+  padding: 4px 10px;
   border-radius: 4px;
   font-size: 0.75rem;
   white-space: nowrap;
   opacity: 0;
   pointer-events: none;
   transition: opacity 150ms;
-  margin-bottom: 4px;
 }
 
-.chapter-marker__tick:hover .chapter-marker__tooltip {
+.chapter-marker__pin:hover .chapter-marker__tooltip {
   opacity: 1;
 }
 

frontend/src/components/ChapterMarkers.tsx

@@ -4,33 +4,65 @@ interface ChapterMarkersProps {
   chapters: Chapter[];
   duration: number;
   onSeek: (time: number) => void;
+  currentTime?: number;
 }
 
+/** Format seconds as m:ss */
+function formatTime(seconds: number): string {
+  if (!Number.isFinite(seconds) || seconds < 0) return "0:00";
+  const m = Math.floor(seconds / 60);
+  const s = Math.floor(seconds % 60);
+  return `${m}:${s.toString().padStart(2, "0")}`;
+}
+
+const PIN_COLOR_CLASS: Record<string, string> = {
+  technique: "chapter-marker__pin--technique",
+  settings: "chapter-marker__pin--settings",
+  reasoning: "chapter-marker__pin--reasoning",
+  workflow: "chapter-marker__pin--workflow",
+};
+
 /**
- * Absolutely-positioned overlay that renders tick marks on the seek bar
- * for each chapter. Ticks are clickable and show a tooltip on hover.
+ * Absolutely-positioned overlay that renders color-coded circle pins
+ * on the seek bar for each chapter. Pins are clickable and show a
+ * rich tooltip on hover. The active pin (matching current playback
+ * position) is enlarged.
  */
-export default function ChapterMarkers({ chapters, duration, onSeek }: ChapterMarkersProps) {
+export default function ChapterMarkers({
+  chapters,
+  duration,
+  onSeek,
+  currentTime,
+}: ChapterMarkersProps) {
   if (!duration || chapters.length === 0) return null;
 
   return (
     <div className="chapter-markers">
       {chapters.map((ch) => {
         const leftPct = (ch.start_time / duration) * 100;
+        const isActive =
+          currentTime != null &&
+          ch.start_time <= currentTime &&
+          currentTime <= ch.end_time;
+
+        const colorClass = PIN_COLOR_CLASS[ch.content_type] ?? "";
+        const activeClass = isActive ? " chapter-marker__pin--active" : "";
+
         return (
           <button
             key={ch.id}
-            className="chapter-marker__tick"
+            className={`chapter-marker__pin${colorClass ? ` ${colorClass}` : ""}${activeClass}`}
             style={{ left: `${leftPct}%` }}
             onClick={(e) => {
               e.stopPropagation();
               onSeek(ch.start_time);
             }}
             aria-label={`Jump to chapter: ${ch.title}`}
-            title={ch.title}
             type="button"
           >
-            <span className="chapter-marker__tooltip">{ch.title}</span>
+            <span className="chapter-marker__tooltip">
+              {ch.title} · {formatTime(ch.start_time)}–{formatTime(ch.end_time)} · {ch.content_type}
+            </span>
           </button>
         );
       })}

frontend/src/components/PlayerControls.tsx

@@ -140,7 +140,7 @@ export default function PlayerControls({ mediaSync, containerRef, chapters }: Pl
           style={{ "--progress": `${seekProgress}%` } as React.CSSProperties}
         />
         {chapters && chapters.length > 0 && (
-          <ChapterMarkers chapters={chapters} duration={duration} onSeek={seekTo} />
+          <ChapterMarkers chapters={chapters} duration={duration} onSeek={seekTo} currentTime={currentTime} />
         )}
       </div>