feat: replace arrowDown markers with ★ stars overlay on chart, colored by category

- InstrumentChart: remove setMarkers arrowDown (level-colored)
  Add DOM overlay div with ★ HTML characters positioned via timeToCoordinate +
  priceToCoordinate(candle.high) - 52px; sized by impact_score; colored by category
  Label (title, 22 chars) rendered above each star; redrawn on scroll/zoom via
  subscribeVisibleLogicalRangeChange; cleaned up on unmount
  ChartEvent interface: add category, impact_score, end_date, description
  Header legend: replace ▼ LT/MT/CT with ★ category color legend
- InstrumentDashboard: remove EventStarsStrip (now internal to chart)
  Remove unused dateToMs helper

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/InstrumentDashboard.tsx

@@ -109,8 +109,6 @@ function fmtDateFR(s: string | null): string {
   return `${d}/${m}/${y}`
 }
 
-function dateToMs(s: string) { return new Date(s).getTime() }
-
 function pctN(a: number | undefined, b: number | undefined): number {
   if (a === undefined || b === undefined || b === 0) return 0
   return ((a - b) / b) * 100
@@ -507,63 +505,6 @@ function NarrativeCard({ narrative, loading, onLoad, instrument }: {
   )
 }
 
-// ── EventStarsStrip — étoiles au-dessus du graphe ────────────────────────────
-
-const CAT_STAR_COLORS: Record<string, string> = {
-  event_calendar: '#f59e0b',  // amber
-  geopolitical:   '#ef4444',  // red
-  fundamental:    '#10b981',  // emerald
-  report:         '#3b82f6',  // blue
-  sentiment:      '#8b5cf6',  // violet
-  technical:      '#06b6d4',  // cyan
-}
-
-function EventStarsStrip({
-  events, priceData,
-}: {
-  events: SnapshotEvent[]
-  priceData: PriceCandle[]
-}) {
-  if (priceData.length < 2 || events.length === 0) return null
-
-  const chartStart = dateToMs(priceData[0].time)
-  const chartEnd   = dateToMs(priceData[priceData.length - 1].time)
-  const totalMs    = chartEnd - chartStart
-  if (totalMs <= 0) return null
-
-  function leftPct(d: string) {
-    return Math.max(0.5, Math.min(98.5, ((dateToMs(d) - chartStart) / totalMs) * 100))
-  }
-
-  return (
-    <div className="relative" style={{ height: 28, paddingRight: 62 }}>
-      {events.map((ev, i) => {
-        const left  = leftPct(ev.date)
-        const color = CAT_STAR_COLORS[ev.category] ?? '#94a3b8'
-        const score = ev.impact_score ?? 0.5
-        const size  = score >= 0.8 ? 16 : score >= 0.6 ? 13 : 11
-        return (
-          <span
-            key={i}
-            className="absolute -translate-x-1/2 select-none cursor-default transition-transform hover:scale-150"
-            style={{
-              left: `${left}%`,
-              bottom: 2,
-              fontSize: size,
-              color,
-              lineHeight: 1,
-              filter: `drop-shadow(0 0 3px ${color}60)`,
-            }}
-            title={`${ev.title}\n${ev.date}${ev.end_date ? ' → ' + ev.end_date : ''}\n${ev.description ?? ''}`}
-          >
-            ★
-          </span>
-        )
-      })}
-    </div>
-  )
-}
-
 // ── DriversPanel — édition inline ────────────────────────────────────────────
 
 function DriversPanel({ instrumentId, drivers, onSave, onClose }: {
@@ -915,11 +856,6 @@ export default function InstrumentDashboard() {
       {/* ── Content ── */}
       {!loading && snapshot && (
         <>
-          <EventStarsStrip
-            events={snapshot.events}
-            priceData={snapshot.price_data}
-          />
-
           <InstrumentChart
             priceData={snapshot.price_data}
             indicators={snapshot.indicators}